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Modern 
Engineering  Practice 

Sc&oat.    a-L 


d 

A  Reference  Library 


ON  ELECTRICITY,   STEAM,   GAS  ENGINES  AND  PRODUCERS,  AUTOMOBILES, 

MARINE    AND     LOCOMOTIVE     WORK,     REFRIGERATION,     PATTERN 

MAKING,  FOUNDRY  WORK,  SHOP  PRACTICE,  TOOL  MAKING, 

FORGING,  MECHANICAL  DRAWING,  MACHINE  DESIGN, 

HEATING,    VENTILATION,     STEAM    FITTING, 

PLUMBING,    ELEVATORS,    ETC. 


Editor-in-  Chief 
FRANK   W.  GUNSAULUS 

PRESIDENT,   ARMOUR  INSTITUTE  OF  TECHNOLOGY 


Assisted  by  a  Corps  of 
DISTINGUISHED   ENGINEERS   AND   TECHNICAL   EXPERTS 


Illustrated  with  ever  Five  Thousand  Engravings 


TWELVE    VOLUMES 


CHICAGO 
AMERICAN   SCHOOL  OF  CORRESPONDENCE 

1908 


COPYRIGHT  1902,  1903,  1905,  1906,  1908  BY 
AMERICAN  SCHOOL  OF  CORRESPONDENCE 


Entered  at  Stationers'  Hall,  London 
All  Rights  Reserved 


Editor-in-Chief 
FRANK    W.   GUNSAULUS 

President,   Armour  Institute  of  Technology 


Authors  and  Collaborators 


F.  B.  CROCKER,  M.  E.,  Ph.  D. 

Head  of  Department  of  Electrical  Engineering,  Columbia  University. 
Past  President,  American  Institute  of  Electrical  Engineers. 


WILLIAM  T.  McCLEMENT,  A.  M. 

Formerly  Professor  of  Chemical  Engineering,  Armour  Institute  of  Technology. 


WILLIAM  ESTY,  S.  B.,  M.  A. 

Head  of  Department  of  Electrical  Engineering,  Lehigh  University. 
Joint  Author  of  "The  Elements  of  Electrical  Engineering." 


VICTOR  C.  ALDERSON,  D.  Sc. 

President,  Colorado  School  of  Mines. 


DUGALD  C.  JACKSON,  B.  S.,  C.  E. 

Head  of  Department  of  Electrical  Engineering,  Massachusetts  Institute  of 
Technology. 


LOUIS  DERR,  S.  B.,  A.  M. 

Associate  Professor  of  Physics,  Massachusetts  Institute  of  Technology. 


HOWARD  M.  RAYMOND,  S.  B. 

Dean  of  Engineering  Studies,  Armour  Institute  of  Technology. 


Authors  and  Collaborators— Continued 


KEMPSTER  B.  MILLER,  M.  E. 

Telephone  Expert  and  Consulting  Engineer.    Author  of  "American  Telephone 
Practice." 


WALTER  S.  LELAND,  S.  B. 

Assistant  Professor  of  Naval  Architecture,  Massachusetts  Institute  of  Technology. 
American  Society  of  Naval  Architects  and  Marine  Engineers. 


GEORGE  C.  SHAAD,  S.  B.,  E.  E. 

Associate  Professor  of  Electrical  Engineering,  Massachusetts  Institute  of  Tech- 
nology. 


CHARLES  DICKERMAN 

Refrigerating  Engineer,  Pennsylvania  Iron  Works  Co. 


FRITZ  LUBBERGER,  E.  E. 

Chief  Engineer,  Automatic  Electric  Co. 
Western  Society  of  Engineers. 


ALBERT  F.  HALL,  S.  B. 

American  Society  of  Mechanical  Engineers. 

American  Society  of  Naval  Architects  and  Marine  Engineers. 

Institute  of  Mechanical  Engineers  of  England. 

German  Society  of  Engineers. 

Associate  Member,  Institute  of  Civil  Engineers  of  England. 


ALFRED  E.  PHILLIPS,  C.  E.,  Ph.  D. 

Professor  of  Civil  Engineering,  Armour  Institute  of  Technology. 
*r* 

CHARLES  THOM 

Chief,  Quadruplex  Department.  Western  Union  Telegraph  Co. 

ARTHUR  L.  RICE,  M.  M.  E. 

Editor  of  "The  Engineer,"  Chicago. 

«!r» 

CHARLES  E.  DURYEA 

First  Vice-President,  American  Motor  League. 
Author  of  "Roadside  Troubles." 


Authors  and  Collaborators— Continued 


FRANCIS  H.  BOYER 

Constructing  Engineer. 

American  Society  of  Mechanical  Engineers. 


LIONEL  S.  MARKS,  S.  B.,  M.  M.  E. 

Assistant  Professor  of  Mechanical  Engineering,  Harvard  University. 
American  Society  of  Mechanical  Engineers. 


SAMUEL  S.  WYER 

Mechanical  Engineer. 

American  Society  of  Mechanical  Engineers. 


WALTER  B.  SNOW,  S.  B. 

Formerly  Mechanical  Engineer,  B.  F.  Sturtevant  Co. 
American  Society  of  Mechanical  Engineers. 


SAMUEL  G.  McMEEN 

Telephone  Expert  and  Consulting  Engineer. 


GEORGE  L.  FOWLER,  A.  B.,  M.  E. 

Consulting  Engineer. 

American  Society  of  Mechanical  Engineers. 

American  Railway  Master  Mechanics'  Association. 


LAWRENCE  K..SAGER,  S.  B.,  M.  P.  L. 

Patent  Attorney  and  Electrical  Expert 
Formerly  Assistant  Examiner,  U.  S.  Patent  Office. 


WILLIAM  C.  BOYRER,  M.  E.,  M.  M.  E. 

Formerly  Division  Engineer,  N.  Y.  and  N.  J.  Telephone  Co. 


WILLIAM  S.  NEWELL,  S.  B. 

With  Bath  Iron  Works,  Bath,  Me. 

Formerly  Instructor,  Massachusetts  Institute  of  Technology. 


ROBERT  V.  PERRY,  S.  B.,  M.  E. 

Associate  Professor  of  Machine  Design,  Armour  Institute  of  Technology. 


Authors  and  Collaborators— Continued 


NATHAN  HASKELL  DOLE 

Editor,  "American  Dictionary  and  Cyclopedia,"  "The  Library  of  the  World's  Best 
'  Literature,"  "The  Literature  of  All  Nations,"  "The  International  Library 
of  Literature,"  etc. 


ALFRED  E.  ZAPF,  S.  B. 

Secretary,  American  School  of  Correspondence. 


WILLIAM  G.  SNOW,  S.  B. 

Steam  Heating  Specialist. 

American  Society  of  Mechanical  Engineers. 

Author  of  "Furnace  Heating,"  etc. 


MAURICE  LEBOSQUET,  s.  B. 

British  Society  of  Chemical  Industry. 
American  Chemical  Society. 


FREDERICK  W.  TURNER 

Instructor  in  Machine  Shop  Work,  Mechanic  Arts  High  School,  Boston. 


JAMES  RITCHEY 

Formerly  Instructor  in  Wood  Working,  Armour  Institute  of  Technology. 


JAMES  R.  CRAVATH 

Western  Editor,  "Street  Railway  Journal,"  Chicago. 


JOHN  C.  SHERMAN,  S.  B. 

Formerly  with  the  Westinghouse  Companies. 


MELVILLE  B.  WELLS,  C.  E. 

Associate  Professor  of   Bridge  and  Structural  Engineering,  Armour  Institute 
of  Technology. 


CHARLES  L.  HUBBARD,  S.  B.,  M.  E. 

Consulting  Engineer  on  Heating,  Ventilating,  Lighting  and  Power. 


Authors  and  Collaborators— Continued 


R.  F.  SCHUCIIARDT,  B.  S. 

Testing  Engineer,  Chicago  Edison  Company. 
^« 

EDWARD  R.  MARKHAM 

Consulting  Mechanical  Engineer. 

Instructor  in  Machine  Shop  Work,  Harvard  University  and  Rindge  Manual 

Training  School. 

Formerly  Superintendent,  Waltham  Watch  Tool  Co. 
American  Society  of  Mechanical  Engineers. 


GEORGE  F.  GEBHARDT,  M.  E.,  M.  A. 

Professor  of  Mechanical  Engineering,  Armour  Institute  of  Technology. 

CHARLES  E.  LORD,  S.  B. 

Manager  of  Patent  Department,  Bullock  Electric  Mfg.  Co. 
^« 

A.  FREDERICK  COLLINS 

Author  of  "Wireless  Telegraphy,  Its  History,  Theory,  and  Practice." 

WM.  C.  STIMPSON 

Head  Instructor  in  Foundry  Work  and  Forging,  Department  of  Science  and 
Technology,  Pratt  Institute. 

EVERETT  E.  KENT,  S.  B.,  LL.  B. 

Counselor-at-Law,  Attorney,  and  Expert  in  Patent  Cases. 

HENRI  F.  CHADWICK,  S.  B. 

President..  Casino  Technical  Night  School,  Pittsburg. 

JOHN  LORD  BACON 

Instructor  in  Forge  Work,  Lewis  Institute,  Chicago. 

ERVIN  KENISON,  S.  B. 

Department  of  Mechanical  Drawing,  Massachusetts  Institute  of  Technology. 


CHARLES  L.  GRIFFIN,  S.  B. 

Mechanical  Engineer,  Semet-Solvay  Co. 

Formerly  Professor  of  Machine  Design,  Pennsylvania  State  College. 

American  Society  of  Mechanical  Engineers. 


Authors  and  Collaborators— Continued 


PERCY  H.  THOMAS,  S.  B. 

Of  Thomas  &  Neall,  Electrical  Engineers,  New  York  Cit., . 
Formerly  Chief  Electrician,  Cooper  Hewitt  Electric  Co. 


RALPH  H.  SWEETSER,  S.  B. 

Superintendent  Algoma  Steel  Co.,  Ltd. 

American  Institute  of  Mining  Engineers. 

Formerly  Instructor,  Massachusetts  Institute  of  Technology. 


ROBERT  A.  MILLIKAN,  Ph.  D. 

Associate  Professor  of  Physics,  University  of  Chicago. 
-*« 

JOHN  H.  JALLINGS 

Mechanical  Engineer. 

*r* 

LLEWELLYN  V.  LUDY,  M.  E. 

Professor  of  Mechanical  Engineering,  Purdue  University. 
American  Society  of  Mechanical  Engineers. 


CHARLES  E.  KNOX,  E.  E. 

Consulting  Electrical  Engineer. 

American  Institute  of  Electrical  Engineers. 


WALTER  H.  JAMES,  S.  B. 

Department  of  Mechanical  Drawing,  Massachusetts  Institute  of  Technology. 
Tr- 

LAWRENCE  S.  SMITH,  S.  B. 

Department  of  Mechanical  Engineering,  Massachusetts  Institute  of  Technology, 

<y- 

NATHAN  R,  GEORGE,  JR.,  A.  M. 

Department  of  Mathematics,  Massachusetts  Institute  of  Technology. 
Tr* 

LOUIS  A.  OLNEY,  A.  C. 

Head  of  Department  of  Textile  Chemistry  and  Dyeing,  Lowell  Textile  School. 
*x» 

HARRIS  C.  TROW,  S.  B.,  Managing  Editor 

Editor  of  Textbook  Department,  American  School  of  Correspondence. 
American  Institute  of  Electrical  Engineers. 


Authorities  Consulted 


THE  editors  have  freely  consulted  the  standard  technical  literature  of 
America  and  Europe  in  the  preparation  of  these  volumes.    They 
desire  to  express  their  indebtedness,  particularly,  to  the  following 
eminent  authorities,   whose  well  known  treatises  should  be  in  the  library 
of  every  engineer. 

Grateful  acknowledgment  is  here  made  also  for  the  invaluable  co-opera- 
tion of  the  foremost  engineering  firms,  in  making  these  volumes  thoroughly 
representative  of  the  best  and  latest  practice  in  the  design  and  construction 
of  steam  and  electrical  machines  and  machine  tools;  also  for  the  valuable 
drawings  and  data,  suggestions,  criticisms,  and  other  courtesies. 


FRANCIS  BACON  CROCKER,  M.  E.,  Ph.  D. 

Head  of  Department  of  Electrical  Engineering,  Columbia  University;  Past  President,  American 

Institute  of  Electrical  Engineers. 
Author  of  "Electric  Lighting,"  "Practical  Management  of  Dynamos  and  Motors." 


SCHUYLER  S.  WHEELER,  D.  Sc. 

Electrical  Expert  of  the  Board  of  Electrical   Control,  New  York  City;  Member  American 

Societies  of  Civil  and  Mechanical  Engineers. 
Author  of  "Practical  Management  of  Dynamos  and  Motors." 

^ 

WILLIAM  M.  BARR 

Member  of  American  Society  of  Mechanical  Engineers. 

Author  of  "Boilers  and  Furnaces,"  "Pumping  Machinery,"  "Chimneys  of  Brick  and  Metal,' 
etc. 

^- 

SIMPSON  BOLLAND 

Author  of  "The  Iron  Founder,"  "The  Iron  Founder's  Supplement." 


HORATIO  A.  FOSTER 

Member  American  Institute  of  Electrical  Engineers;  American  Society  of   Mechanical 

gineers.     Consulting  Engineer. 
Author  of  "Electrical  Engineer's  Pocketbook." 


J.  FISHER-HINNEN 

Late  Chief  of  the  Drawing  Department  at  the  Oerlikon  Works. 
Author  of  "Continuous-Current  Dynamos." 


WILLIAM  F.  DURAND,  Ph.  D. 

Formerly  Professor  of  Marine  Engineering,  Cornell  University. 

Author  of  "Resistance  and  Propulsion  of  Ships,"  "Practical  Marine  Engineering. 


W.  H.  FORD,  M.  E. 

Author  of  "Boiler  Making  for  Boiler  Makers." 


Authorities  Consulted— Continued 


ROBERT  GRIMSHAW,  M.  E. 

Author  of  "Steam  Engine  Catechism."  "Boiler  Catechism,"  "Locomotive  Catechism, "  "Engine 
Runner's  Catechism,"  "Shop  Kinks."  etc. 

^ 

GARDNER  D.  HISCOX,  M.  E. 

Author  of   "Gas,  Gasoline,  and  Oil  Engines." 

V 

GEORGE  C.  V.  HOLMES 

Whitworth  Scholar:  Secretary  of  the  Institute  of  Naval  Architects,  etc. 
Author  of  "The  Steam  Engine." 

«r« 

ROBERT  ANDREWS  MILLIKAN,  Ph.  D. 

Associate  Professor  of  Physics  in  the  University  of  Chicago. 
Joint  Author  of  "A  First  Course  in  Physics." 

V 

WILLIAM  KENT,  M.  E. 

Consulting  Engineer;  Member  of  American  Society  of  Mechanical  Engineers,  etc. 
Author  of    "Strength    of  Materials,"    "Mechanical   Engineer's    Pocketbook,"    "Steam   Boiler 
Economy,"  etc. 

rx- 

DUGALD  C.  JACKSON,  B.  S.,  C.  E. 

Head  of  Department  of  Electrical  Engineering,  Massachusetts  Institute  of  Technology:  Member 
of  American  Society  of  Mechanical  Engineers;  American  Institute  of  Electrical  Engineers. 

Author  of  "A  Textbook  on  Electromagnetism  and  the  Construction  of  Dynamos,"  "Alternating 
Currents  and  Alternating-Current  Machineiy." 

*r» 

JOHN  PRICE  JACKSON 

Professor  of  Electrical  Engineering,  Pennsylvania  State  College;  Member  of  American  Institute 

of  Electrical  Engineers. 
Author  of  "Alternating  Currents  and  Alternating-Current  Machinery.' 

V^ 

GAETANO  LANZA,  S.  B.,  C.  E.,  M.  E. 

Prof essor  of  Theoretical  and  Applied  Mechanics,  Massachusetts  Institute  of  Technologv  Mem- 
ber of  American  Society  of  Mechanical  Engineers,  etc. 
Author  of  "Applied  Mechanics." 

Tr. 

C.  W.  MACCORD,  A.  M. 

Prof  essor  of  Mechanical  Drawing,  Stevens  Institute  of  Technology 
Author  of  "Movement  of  Slide  Valves  by  Eccentrics." 

^« 

MANSFIELD  MERRIMAN,  Ph.  D. 

Professor    of    Civil    Engineering.   Lehigh  University;    Member  of  American  Society  of  Civil 
Author    of    "Mechanics    of    Materials,"    "Treatise    on   Hydraulics,"    "Elements    of    Sanitary 

^ 

CECIL  H.  PEABODY,  S.  B. 

Professor  of  Marine  Engineering  and  Naval  Architecture,  Massachusetts  Institute  of 
Technology. 

Author  of  "Thermodynamics  of  the  Steam  Engine,"  "Tables  of  the  Properties  of  Saturated 
Bolters'  "  FS  t0  Steam  Eneines,"  "Manual  of  Steam  Engine  Indicators,"  "Steam 


Authorities  Consulted— Continued 


EDWARD  F.  MILLER 

Professor  of  Steam  Engineering,  Massachusetts  Institute  of  Technology. 
Author  of  "Steam  Boilers." 

^- 

WILLIAM  JOHN  MACQUORN  RANKINE,  LL.  D.,  F.  R.  S.  S. 

Civil  Engineer;  Late  Regius  Professor  of  Civil  Engineering  and  Mechanics  in  the  University  of 

Glasgow,  etc. 
Author  of  "Applied  Mechanics,"  "The  Steam  Engine,"  "Civil  Engineering,"  "Useful  Rules  and 

Tables,"  'Machinery  and  Mill  Work,"  "A  Mechanical  Textbook." 
*• 

KEMPSTER  B.  MILLER,  M.  E. 

Consulting  Engineer,  and  Telephone  Expert. 
Author  of  "American  Telephone  Practice." 

*• 

MAURICE  A.  OUDIN,  M.  S. 

Member  of  American  Institute  of  Electrical  Engineers. 
Author  of  "Standard  Polyphase  Apparatus  and  Systems." 

**• 

IRA  REMSEN,  M.  D.,  Ph.  D.,  LL.  D. 

President  of  Johns  Hopkins  University,  and  Professor  of  Chemistry,  etc. 

Author  of  "Principles  of  Theoretical  Chemistry,"  "Introduction  to  the  Study  of  the  Compounds 
of  Carbon,"  "The  Elements  of  Chemistry,"  "Inorganic  Chemistry,"  etc. 

^« 

WILLIAM  RIPPER 

Professor  of  Mechanical  Engineering  in  the  Sheffield  Technical  School;  Member  of  the  Institute 

of  Mechanical  Engineers. 
\uthor  of  "Machine  Drawing  and  Design,"  "Practical  Chemistry,"  "Steam,"  etc. 

^* 

JOSHUA  ROSE,  M.  E. 

Author  of  "Mechanical  Drawing  Self-Taught,"  "Modern  Steam  Engineering,"  "Steam  Boilers," 
"The  Slide  Valve,"  "Pattern  Maker's  Assistant,"  "Complete  Machinist,"  etc. 
*• 

LAMAR  LYNDON,  B.  E.,  M.  E. 

Consulting   Electrical    Engineer;   Associate   Member   of   American    Institute   of    Electrical 

Engineers;  Member  of  American  Electro-Chemical  Society. 
Author  of  "Storage  Battery  Engineering." 

•>• 

ROBERT  H.  THURSTON,  C.  E.,  Ph.  B.,  A.  M.,  LL.  D. 

Late  Director  of  Sibley  College  of  Engineering,  Cornell  University. 

Author  of  "Manual  of  the  Steam  Engine,"  "Manual  of  Steam  Boilers,"  "History  of  the  Steam 
Engine,"  etc. 

"*" 

SILVANUS  P.  THOMPSON,  D.  Sc.,  B.  A.,  F.  R.  S.,  F.  R.  A.  S. 

Principal  and  Professor  of  Physics  in  the  City  and  Guilds  of  London  Technical  College. 
Author  of  "Electricity  and  Magnetism,"  "Dynamo-Electric  Machinery,"  "Polyphase  Electric 
Currents,"  "Electromagnet,"  etc. 

^» 

W.  S.  FRANKLIN  and  R.  G.  WILLIAMSON 

Joint  Authors  of  "The  Elements  of  Alternating  Current." 


Authorities  Consulted— Continued 


EDWARD  R.  MARKHAM 

Instructor  in  Machine  Shop  Work,  Harvard  University  and  Rindge  Manual  Training  School; 

Formerly  Superintendent  Waltham  Watch  Tool  Co. 
Author  of  "The  American  Steel  Worker." 

TT» 

SAMUEL  EDWARD  WARREN 

Late  Professor  of  Descriptive  Geometry  and  Drawing,  Massachusetts  Institute  of  Technology. 

Author  of  "General  Problems  in  Shades  and  Shadows,"  "Shadows  and  Perspective,"  "Higher 

General  Problems  with  Linear  Perspective  of  Form,"  "Shadow  and  Reflection,"  etc. 


THOMAS  D.  WEST 

Practical  Moulder  and  Foundry  Manager;  Member,  American  Society  of  Mechanical  Engineers. 
Author  of  "American  Foundry  Practice." 

^ 

ROBERT  WILSON 

Author  of  "Treatise  on  Steam  Boilers."  "Boiler  and  Factory  Chimneys,"  etc. 


JAMES  J.  LAWLER 

Author  of  "Modern  Plumbing,  Steam  and  Hot  Water  Heating." 


WILLIAM  C.  UNWIN,  F.  R.  S.,  M.  Inst.  C.  E. 

Professor  of  Civil  and  Mechanical  Engineering,  Central  Technical  College,  City  and  Guilds  of 

London  Institute,  etc. 
Author  of  "Machine   Design,"  "The  Development  and  Transmission  of   Power  from  Central 

Stations,"  etc. 

r>* 

WILLIAM  ESTY,  S.  B.,  M.  A. 

Head  of  Department  of  Electrical  Engineering,  Lehigh  University. 
Joint  Author  of  "The  Elements  of  Electrical  Engineering." 


WILLIAM  H.  VAN  DERVOORT,  M.  E. 

Author  of  "Modern  Machine  Shop  Tools." 

V 

J.  A.  EWING,  M.  A.,  B.  Sc.,  F.  R.  S.,  M.  Inst.  C.  E. 

Professor  of  Mechanism  and  Applied  Mechanics  in  the  University  of  Cambridge. 
Author  of  "The  Steam  Engine  and  Other  Heat  Engines." 


A.  E.  SEATON 

Author  of  "A  Manual  of  Marine  Engineering." 

ROLLA  C.  CARPENTER,  M.  S.,  C.  E.,  M.  M.  E. 

Professor  of  Experimental  Engineering,  Cornell  University;  Member,  American  Society  of  Heat- 
ing and  Ventilating  Engineers;  Member,  American  Society  of  Mechanical  Engineers. 
Author  of  "Heating  and  Ventilating  Buildings." 


Table   of  Contents 


VOLUME  XI 
MACHINE  DESIGN       .        .        .        .        .        By  C.  L.  Griffin^       Page  *11 

Principles  and  Methods  —  Mechanical  Thought  —  Invention  —  Use  of  Handbooks 

—  Calculations  and  Notes  —  Sketches  —  Theoretical  Design  —  Practical  Modifica- 
tion —  Delineation   and   Specification  —  Constructive   Mechanics  —  Forces  and 
Moments  —  Tension,  Compression,  Torsion  —  Friction  and  Lubrication  —  Work- 
ing Stresses  and  Strains  —  Designing  an  Elevator  Wire-Rope  Drive  —  Reversed 
Machine  Design  —  Classification  of  Machinery  —  Machine  Tools  (Lathe,  Planer, 
Milling  Machine,  etc.)  —  Motive- Power  Machinery  (Steam  Engine,  Air-Compres- 
sor,  etc.)  — Structural   Machinery  (Cranes,   Elevators,  Cars,  etc.)— Mill  and 
Plant  Machinery  (Rolls,  Crushers,  Drills,  etc.) — Cast  and  Wrought  Iron  and 
Steel  —  Original  Design  —  Design  of  Component  Parts  of  Machinery 

HEATING  AND  VENTILATION         .         .         By  C.  L.  Hubbard       Page  197 

Systems  of  Warming  —  Hot- Air  Furnaces  —  Direct  and  Indirect  Steam  and  Hot- 
Water  Heating  —  Radiators  —  Exhaust  Steam  Heating  —  Ventilation  —  Heat 
Losses  —  Direct-  and  Indirect-Draft  Furnaces  —  Furnace  Details  —  Smoke-Pipes 

—  Flues  —  Cold-Air   Box  —  Warm- Air    Pipes  —  Registers  —  Circulation   Coils  — 
Systems   of   Piping  —  Air- Valves  —  Vacuum    Systems  —  Fans   and    Blowers  — 
Factory  Heating  —  Electric  Heating — Automatic  Regulators  —  Air-Filters  and 
Washers  — Heating  and  Ventilating  Schools,  Churches,  etc. 

PLUMBING        .        .        .        .       .        .       By  C.  L.  Hubbard       Page  411 

Fixtures  —  Bathtubs  —  Water-Closets  —  Urinals  —  Lavatories  —  Sinks  —  Traps  — 
Tanks — Faucets  —  Soil  and  Waste  Pipes  —  Tile  Pipes  —  Cesspools  —  Traps  and 
Vents  —  Siphonage  —  Back  and  Local  Venting  —  Fresh- Air  Inlets  —  Foul- Air 
Outlets  —  Sewage  Disposal  —  Pipe  Connections  (Bathroom,  Kitchen  Sink)  —  Pipe 
Sizes  —  Plumbing  for  Dwelling  Houses ;  for  Apartment  Houses;  for  Hotels;  for 
Railroad  Stations;  for  Schoolhouses ;  for  Shops  and  Factories  —  Testing  and 
Inspection  —  Sewerage  Systems  (Separate,  Combined)  —  Manholes  —  Flushing 
Devices  —  Ventilation  of  Sewers  —  Catch-Basins  —  Storm  Overflows  —  Pumping 
Stations  —  Tidal  Chambers  —  Sewage  Purification  —  Sedimentation  —  Mechan- 
ical Straining  —  Chemical  Precipitation  —  Irrigation  —  Intermittent  Filtration 

—  Domestic  Water  Supply  —  Pumps  —  Storage  Tanks  —  Water-Backs  —  Circula- 
tion  Pipes  —  Temperature  Regulators  —  Gas  Fitting  —  Testing   Installation  — 
Gas  Fixtures  —  Gas  Heating  and  Cooking  —  Gas  Meters  —  Gas  Machines 

REVIEW  QUESTIONS Page  525 

INDEX       .  Page  539 


*For  page  numbers,  see  foot  of  pages. 

tFor  professional  standing  of  authors,  see  list  of  Authors  and  Collaborators  at 
front  of  volume. 


PRINCIPLE  OF  HOT  WATER  HEATING  ILLUSTRATED  BY  TRANSVERSE  SECTIONAL 
VIEW  SHOWING  BOILER,  RADIATOR  AND  EXPANSION  TANK, 

American  Radiator  Company. 


it  111 


MACHINE  DESIGN, 


PART  I. 

Definition.  Machine  Design  is  the  art  of  mechanical  thought 
development,  and  specification. 

It  is  an  art,  in  that  its  routine  processes  can  be  analyzed  and 
systematically  applied.  Proficiency  in  the  art  positively  cannot 
be  attained  by  any  "  short  cut "  method.  There  is  nothing  of  a 
spectacular  nature  in  the  methods  of  Machine  Design.  Large 
results  cannot  be  accomplished  at  a  single  bound,  and  success  is 
possible  only  by  a  patient,  step-by-step  advance  in  accordance 
with  well-established  principles. 

"  Mechanical  thought "  means  the  thinking  of  things  strictly 
from  their  mechanical  side;  a  study  of  their  mechanical  theory, 
structure,  production,  and  use;  a  consideration  of  their  mechanical 
fitness  as  parts  of  a  machine. 

"  Mechanical  development "  signifies  the  taking  of  an  idea  in 
the  rough,  in  the  crude  form,  for  example,  in  which  it  comes  from 
the  inventor,  working  it  out  in  detail,  and  refining  and  fixing  it  in 
shape  by  the  designing  process.  Ideas  in  this  way  may  become 
commercially  practicable  designs. 

"Mechanical  specification"  implies  the  detailed  description 
of  designs,  in  such  exact  form  that  the  shop  workmen  are  enabled 
to  construct  completely  and  put  in  operation  the  machines  repre- 
sented in  the  designs. 

The  object  of  Machine  Design  is  the  creation  of  machinery 
for  specific  purposes.  Every  department  of  a  manufacturing 
plant  is  a  controlling  factor  in  the  design  and  production  of  the 
machines  built  there.  A  successful  desio-n  cannot  be  out  of 

O 

harmony  with  the  organized  methods .  of  production.  Hence  in 
the  high  development  of  the  art  of  Machine  Design  is  involved  a 
knowledge  of  the  operations  in  all  the  departments  of  a  manu- 
facturing plant.  The  student  is  therefore  urged  not  only  to 
familiarize  himself  with  the  direct  production  of  machinery,  but  to 
study  the  relatiou  thereto  of  the  allied  commercial  departments 


11 


MACHINE  DESIGN 


IK-  should  get  into  the  spirit  of  business  at  the  start,  get  into  the 
shop  atmosphere,  execute  his  work  just  as  though  the  resulting 
design  were  to  be  built  and  sold  in  competition.  He  should  visit 
shops,  work  in  them  if  possible,  and  observe  details  of  design  and 
methods  of  finishing  machine  parts.  In  this  way  he  will  begin 
to  store  up  bits  of  information,  practical  and  commercial,  which 
will  have  valuable  bearing  on  his  engineering  study. 

The  labor  involved  in  the  design  of  a  complicated  automatic 
machine  is  evidenced  by  the  designer's  wonderful  familiarity  with 
:is  every  detail  as  he  stands  before  the  complete*1  machine  in 
operation  and  explains  its  movements  to  an  observer.  The  intri- 
cate mass  of  levers,  shafts,  pulleys,  gears,  cams,  clutches,  etc.,  etc., 
packed  into  a  small  space,  and  confusing  even  to  a  mechanical 
mind,  seems  like  a  printed  book  to  the  designer  of  them. 

This  is  so  because  it  is  a  familiar  journey  for  the  designer's 
mind  to  run  over  a  path  which  it  has  already  traversed  so  many 
times  that  he  can  see  every  inch  of  it  with  his  eyes  shut.  Every 
detail  of  that  machine  has  been  picked  from  a  score  or  more  of 
possible  ideas.  One  by  one,  ideas  have  been  worked  out,  laid 
aside,  and  others  taken  up.  Little  by  little,  the  special  fitness  of 
certain  devices  has  become  established,  but  only  by  patient,  care- 
ful consideration  of  others,  which  at  first  seemed  equally  good. 

Every  line,  and  corner,  and  surface  of  each  piece,  however 
small  that  piece  may  be,  has  been  through  the  refining  process  of 
theoretical,  practical,  and  commercial  design.  Every  piece  has 
been  followed  in  the  mind's  eye  of  its  designer  from  the  crude 
material  of  which  it  is  made,  through  the  various  processes  of  fin- 
\shing,  to  its  final  location  in  the  completed  machine;  thus  its 
bodily  existence  there  is  but  the  realization  of  an  old  and  familiar 
picture. 

AVhat  wonder  that  the  machine  seems  simple  to  the  designer 
of  it!  As  he  looks  back  to  the  multitude  of  ideas  invented, 
worked  out,  considered  and  discarded,  the  machine  in  its  final 
form  is  but  a  trifle.  It  merely  represents  a  survival  of  the  fittest. 

No  successful  machine,  however  simple,  was  ever  designed 
that  did  not  go  through  this  slow  process  of  evolution.  No 
machine  ever  just  simply  happened  by  accident  to  do  the  work 
for  which  it  is  valued.  No  other  principle  upon  which  the  suc- 


12 


MACHINE  DESIGN  5 

cessful  design  of  machinery  depends  is  so  important  as  this  careful, 
patient  consideration  of  detail.  A  machine  is  seldom  unsuccessful 
because  some  main  point  of  construction  is  wrong.  .  The  principal 
features  of  a  machine  are  usually  the  easiest  to  determine.  It  is 
a  failure  because  some  little  detail  was  overlooked,  or  hastily  con- 
sidered, or  allowed  to  be  neglected,  because  of  the  irksome  labor 
necessary  to  work  it  out  properly. 

There  is  no  task  so  tedious,  for  example,  as  the  devising  of 
the  method  of  lubricating  the  parts  of  a  complicated  machine. 
Yet  there  is  no  point  of  design  so  vital  to  its  life  and  operation  as 
an  absolute  assurance  of  an  adequate  supply  of  oil  for  the  moving 
parts  at  all  times  and  under  all  circumstances.  Suitable  means 
often  cannot  be  found,  after  the  parts  are  together,  hence  the 
machine  goes  into  service  on  a  risky  basis,  with  the  result,  per- 
haps, of  early  failure,  due  to  "running  dry."  Good  designers 
will  not  permit  a  design  to  leave  their  hands  which  does  not  pro- 
vide practically  automatic  oiling,  or  at  least  such  means  of  lubri- 
cation that  the  operator  can  offer  no  excuse  for  neglecting  to  oil 
his  machine.  This  is  but  a  single  illustration  of  many  which 
might  be  presented  to  impress  the  definite  and  detail  character 
necessary  in  work  in  Machine  Design. 

Relation.  The  relation  which  Machine  Design  should  cor- 
rectly bear  to  the  problems  that  it  seeks  to  solve,  is  twofold;  and 
there  are,  likewise,  two  points  of  view  corresponding  to  this  two- 
fold relation,  from  which  a  study  of  the  subject  should  be  traced. 
Neither  of  these  can  be  discarded  and  an  efficient  mastery  of  the 
art  attained.  These  points  are — 
I.  Theory. 

II.    Production. 

I.  Theory.  From  this  point  of  view,  Machine  Design  is 
merely  a  skeleton  or  framework  process,  resulting  in  a  repre- 
sentation of  ideas  of  pure  motion,  fundamental  shape,  and  ideal 
proportion.  It  implies  a  working  knowledge  of  physical  and 
mathematical  laws.  It  is  a  strictly  scientific  solution  of  the 
problem  at  hand,  and  may  be  based  purely  on  theory  which  has 
been  reasoned  out  by  calculation  or  deduced  from  experiment. 
This  is  the  only  sure  foundation  for  intelligent  design  of  any  sort. 

But  it  is  not  enough  to  view  the  subject  from  the  standpoint 


MACHINE  DESIGN 


of  theory  alone.  If  we  stopped  here  we  should  have  nothing  but 
mechanisms,  mere  laboratory  machines,  simply  structures  of 
itiovnuit  v  ami  examples  of  line  mechanical  skill.  A  machine  may 
lu;  correct  in  the  theory  of  its  motions;  it  may  be  correct  in  the 
theoretical  proportions  of  its  parts;  it  may  even  be  correct  in  its 
operation  for  the  time  being;  and  yet  its  complication,  its  mis- 
directed and  wasteful  effort,  its  lack  of  adjustment,  its  expensive 
and  irregular  construction,  its  lack  of  compactness,  its  difficulty 
of  ivudv  repair,  its  inability  to  hold  its  own  in  competition — any 
of  these  may  thro\v  the  balance  to  the  side  of  failure.  Such  a 
machine,  commercially  considered,  is  of  little  value.  No  shop 
will  build  it,  no  machinery  house  will  sell  it,  nobody  will  buy  it 
if  it  is  put  on  the  market. 

Thus  we  see  that,  aside  from  the  theoretical  correctness  oi 
principle,  the  design  of  a  machine  must  satisfy  certain  other 
exacting  requirements  of  a  distinctly  business  nature. 

IT.  Production,  From  this  point  of  view,  Machine  Design 
is  the  practical,  marketable  development  of  mechanical  ideas. 
viewed  thus,  the  theoretical,  skeleton  design  must  be  so  clothed 
and  shaped  that  its  production  may  be  cheap,  involving  simple 
and  efficient  processes  of  manufacture.  It  must  be  judged  by  the 
latest  shop  methods  for  exact,  and  maximum  output.  It  must 
possess  all  the  good  points  of  its  competitor,  and,  withal,  some 
novel  and  valuable  ones  of  its  own.  In  these  days  of  keen  com- 
petition it  is  only  by  carefully  studied,  well-directed  effort  toward 
raj »id,  efficient,  and,  therefore,  cheap  production  that  any  machine 
can  be  brought  to  a  commercial  basis,  no  matter  what  its  other 
merits  may  be.  All  this  must  be  thought  of  and  planned  for  in 
the  design,  and  the  final  shapes  arrived  at  are  quite  as  much  a 
result  of  this  second  point  of  view  as  of  the  first. 

As  a  good  illustration  of  this,  may  be  cited  the  effect  of  the 
present  somewhat  remarkable  development  of  the  so-called  '-high 
sj)eed ''  steels.  The  speeds  and  feeds  possible  with  tools  made  of 
these  steels  are  such  that  the  driving  power,  gearing' and  feed 
mechanism  of  the  ordinary  lathe  are  wholly  inadequate  to  the 
demands  made  upon  tliem  when  working  the  tool  to  its  limit. 
This  means  that  the  basis  of  design  as  used  for  the  ordinary  tool 
steel  will  not  do,  if  the  machine  is  expected  to  stand  up  to  the 


i  i 


MACHINE  DESIGN 


cuts  possible  with  the  new  steels.  Hence,  while  the  old  designs 
were  right  for  the  old  standard,  a  new  one  has  been  set,  and  a 
thorough  revision  on  a  high-speed  basis  is  imminent,  else  the 
market  for  them  as  machines  of  maximum;  output  will'  be  lost. 

From  these  definitions  it  is  evident  that  the  designer  must 
not  only  use  all  the  theory  at  his  command,  but  must  continually 
inform  himself  on  all  processes  and  conditions  of  manufacture, 
and  keep  an  eye  on  the  tende~"y  of  the  sales  markets,  both 
of  raw  material  and  the  finished  machinery  product.  This  is 
what  in  the  broadest  sense  is  meant  by  the  term  "  Mechanical 
Thought,"  thought  which  is  directed  and  controlled,  not  only  by 
theoretical  principle  but  by  closely  observed  practice.  From  the 
feeblest  pretenders  of  design  to  those. engineers  who  consummate 
the  boldest  feats  and  control  the  largest  enterprises,  the  process 
which  produces  results  is  always  the  same.  Although  experience 
is  necessary  for  the  best  mechanical  judgment,  yet  the  studen.t 
must  at  least  begin  to  cultivate  good  mechanical  sense  very  early 
in  his  study  of  design. 

Invention.  Invention  is  closely  related  to  Machine  Design, 
but  is  not  design  itself.  Whatever  is  invented  has  yet  to  be 
designed.  An  invention  is  of  little  value  until  it  has  been  refined 
by  the  process  of  design. 

Original  design  is  of  an  inventive  nature,  but  is  not  strictly 
invention.  Invention  is  usually  considered  as  the  result  of  genius, 
and  is  announced  in  a  flash  of  brilliancy.  We  see  only  the  flash, 
but  behind  the  flash  is  a  long  course  of  the  mosl  concentrated 
brain  effort.  Inventions  are  not  spontaneous,  are  not  thrown  off 
like  sparks  from  the  blacksmith's  anvil,  but  are  the  result  of  hard 
and  applied  thinking.  This  is  worth  noting  carefully,  for  the 
same  effort  which  produces  original  design  may  develop  a  valuable 
invention.  But  there  is  little  possibility  of  inventing  anything 
except  through  exhaustive  analysis  and  a  clear  interpretation  of 
such  analysis. 

Handbooks  and  Empirical  Data.  The  subject  matter  in 
these  is  often  contradictory  in  its  nature,  but  valuable  nevertheless. 
Empirical  data  are  data  for  certain  fixed  conditions  and  are  not 
general.  Hence,  when  handbook  data  are  applied  to  some  specific 
case  of  design,  while  the  information  should  be  used  in  the  freest 


8  MACHINE  DESIGN 

manner,  yet  it  must  not  be  forgotten  that  the  case  at  hand  is  prob- 
ably different,  in  some  degree,  from  that  upon  which  the  data  were 
based,  and  unlike  any  other  case  which  ever  existed  or  will  ever 
afain  exist.  Therefore  the  data  should  be  applied  with  the  greatest 
discretion,  and  when  so  applied  will  contribute  to  the  success  of 
the  design  at  least  as  a  check,  if  not  as  a  positive  factor. 

The  student  should  at  the  outset  purchase  one  good  handbook, 
and  acquire  the  habit  of  consulting  it  on  all  occasions,  checking 
and  comparing  his  own  calculations  and  designs  therefrom.  Care 
must  be  taken  not  to  become  tied  to  a  handbook  to  such  an  extent 
that  one's  own  lesults  are  wholly  subordinated  to  it.  Independence 
in  design  must  be  cultivated,  and  the  student  should  not  sacrifice 
his  calculated  results  until  they  can  be  shown  to  be  false  or  based 
on  false  as>umption.  Originality  and  confidence  in  design  will  be 
the  result  if  this  course  be  honestly  pursued. 

Calculations,  Notes,  and  Records.  Accurate  calculations  are 
the  basis  of  correct  proportions  of  machine  parts.  There  is  aright 
way  to  make  calculations  and  a  wrong  way,  and  the  student  will 
usually  take  the  wrong  way  unless  he  is  cautioned  at  the  start. 

The  wrong  way  of  making  calculations  is  the  loose  and  shift- 
less fashion  of  scratching  upon  a  scrap  of  detached  paper  marks 
aiid  figures,  arranged  in  haphazard  form,  and  disconnected  and 
incomplete.  These  calculations  are  in  a  few  moments'  time  totally 
meaningless,  even  to  the  author  of  them  himself,  and  are  so  easily 
lost  or  mislaid  that  when  wanted  they  usually  cannot  be  found. 

Engineering  calculations  should  always  be  made  systemati- 
cally, neatly,  and  in  perfectly  legible  form,  in  some  permanently 
bound  blank  book,  so  that  reference  may  always  be  had  to  them  at 
any  future  time  for  the  purpose  of  checking  or  reviewing.  Put 
all  the  data  down.  Do  not  leave  in  doubt  the  exact  conditions 
under  which  the  calculations  were  made.  Note  the  date  of  calcu- 
lation. 

Jf  a  mistake  in  figures  is  made,  or  a  change  is  found  neces- 
sary, never  rub  out  the  figures  or  tear  out  the  leaf,  or  in  any  way 
obliterate  the  figures.  Simply  draw  a  bold  cross  through  the  wrong 
part  and  begin  again.  Often  a  calculation  which  is  supposed  to 
be  wrong  is  later  shown  to  be  right,  or  the  facts  which  caused  the 
error  ID  ay  be  needed  for  investigatior  and  comparison.  Time  which 


MACHINE  DESIGN  9 


is  spent  in  making  figures  is  always  valuable  time,  time  too  pre- 
cious to  be  thrown  away  by  destroying  the  record. 

The  recording  of  calculations  in  a  permanent  form,  as  just 
described,  is  the  general  practice  in  all  modern  engineering  offices. 
This  plan  has  been  established  purely  as  a  business  policy.  In 
case  of  error  it  locates  responsibility  and  settles  dispute.  Con- 
sistent designing  is  made  possible  through  the  records  of  past 
designs.  Proposals,  estimates,  and  bids  may  often  be  made 
instantly,  on  the  basis  of  what  these  record  books  show  of  sizes 
and  weights.  This  bookkeeping  of  calculations  is  as  important  a 
factor  of  systematic  engineering  as  bookkeeping  of  business 
accounts  is  of  financial  success. 

The  student  should  procure  for  this  purpose  a  good  blank  book 
with  a  firm  binding,  size  of  page  not  smaller  than  6  by  8  inches 
(perhaps  8  by  11  inches  may  be  better),  and  every  calculation,  how- 
ever small  and  apparently  unimportant,  should  be  made  in  it. 

Sample  pages  of  engineering  calculations  are  reproduced  in 
Eigs.  3  to  9.  Note  the  sketch  showing  the  forces.  Note  the  clear 
statement  of  data.  Note  the  systematic  writing  of  the  equations, 
and  the  definite  substitutions  therein.  Note  the  heavy  double 
underscoring  of  the  result,  when  obtained.  There  is  nothing  in 
the  whole  process  of  the  calculation  that  cannot  be  reviewed  at 
any  moment  by  anybody,  and  in  the  briefest  time. 

The  development  of  a  personal  note-book  is  of  great  value  to 
the  designer  of  machinery.  The  facts  of  observation  and  experi- 
ence recorded  in  proper  form,  bearing  the  imprint  of  intimate 
personal  contact  with  the  points  recorded,  cannot  be  equalled 
in  value  by  those  of  any  hand  or  reference  book  made  by  another. 
There  is  always  a  flavor  about  a  personal  note-book,  a  sort  of 
guarantee,  which  makes  the  use  of  it  by  its  author  definite  and 
sure. 

The  habit  of  taking  and  recording  notes,  or  even  knowing 
what  notes  to  take,  is  an  art  in  itself,  and  the  student  should 
begin  early  to  make  his  note-book.  Aside  from  the  value  of  the 
notes  themselves  as  a  part  of  his  personal  equipment,  the  facility 
,v:.iii  which  his  eye  will  be  trained  to  see  and  record  mechanical 
things  will  be  of  great  value  in  all  of  his  study  and  work.  How 
many  men  go  through  a  shop  and  really  see  nothing  of  the  opera- 


17 


10  MACHINE  DESIGN 

tions  going  on  therein,  or,  seeing  them,  remember  nothing  !  "An 
engineer,  trained  in  this  respect,  will  to  a  surprising  degree  be 
able  to  retain  and  sketch  little  details  which  fall  under  his  eye  for 
a  brief  moment  only,  while  he  is  passing  through  a  crowded  shop. 

Some  draftsmen  have  the  habit  of  copying  all  the  standard 
tables  of  the  various  offices  in  which  they  work.  "While  these  are 
of  some  value  in  a  few  cases,  yet  this  is  not  what  is  meant  by  a 
good  note-book  in  the  best  sense.  Ideas  make  a  good  note-book, 
not  a  mere  tabulation  of  figures.  If  the  basis  upon  which  stan- 
dards are  founded  can  be  transferred  to  permanent  personal  record, 
or  novel  methods  of  calculation,  or' simple  features  of  construc- 
tion, or  data  of  mechanical  tests,  or  efficient  arrangement  of 
machinery — if  tlu*c  can  be  preserved  for  reference,  the  note-book 
will  be  of  greatest  value. 

Whatever  is  noted  down,  make  clear  and  intelligible,  illus- 
trating by  a  sketch  if  possible.  Make  the  cote  so  clear  that 
reference  to  it  after  a  long  space  of  years  would  bring  the  whole 
subject  before  the  mind  in  an  instant.  If  this  is  not  done  the 
author  of  the  note  himself  will  not  have  patience  to  dig  out  the 
meaning  when  it  is  needed;  and  the  note  will  be  of  no  value. 

METHOD   OF   DESIGN. 

The  fundamental  lines  of  thought  and  action  which  every 
designer  follows  in  the  solution  of  any  problem  in  any  class  of 
work  whatsoever,  are  four  in  number.  The  expert  may  carry  all 
these  in  mind  at  the  same  time,  without  definite  separation  into  a 
a  step- by-step  process;  but  the  student  must  master  them  in  their 
proper  sequence,  and  thoroughly  understand  their  application. 
In  these  four  are  concentrated  the  entire  art  of  Machine  Design. 
When  they  have  become  so  familiar  as  to  be  instinctively  applied 
on  any  and  all  occasions,  good  design  is  the  result.  The  only 
other  quality  which  will  facilitate  still  further  the  design  of  good 
machinery  is  experience;  and  that  cannot  be  taught,  it  must  be 
acquired  by  actual  work. 

i.  Analysis  of  Conditions  and  Forces.  First,  take  a  good 
square  look  at  the  problem  to  be  solved.  Study  it  from  all  sides, 
view  it  in  all  lights,  note  the  worst  conditions  which  can  possibly 
exist,  note  the  average  conditions  of  service,  note  any  special  or 
irregular  service  likely  to  be  called  for. 


:  - 


MACHINE  DESIGN  11 

"With  these  conditions  well  in  mind,  make  a  careful  analysis 
of  all  the  forces,  maximum  as  well  as  average,  which  may  be 
brought  into  play.  Make  a  rough  sketch  of  the  piece  under  con- 
sideration, and  put  in  these  forces.  Be  sure  that  these  forces  are 
at  least  approximately  right.  Go  over  the  analysis  carefully 
again  and  again.  Remember  that  time  saved  at  the  beginning 
by  hasty  and  poor  analysis  will  actually  be  time  lost  at  the  end; 
and  if  the  machine  actually  fails  from  this  reason,  heavy  financial 
loss  in  material  and  labor  will  occur.  Any  haste  toward  com- 
pletion of  the  structure  beyond  the  roughest  outline,  without  this 
careful  study  of  forces,  is  a  blind  leap  in  the  dark,  entirely  un- 
scientific, and  almost  certain  to  result  in  ultimate  failure. 

On  the  other  hand  this  principle  may  be  carried  too  far.  In 
trying  to  make  the  analysis  thorough  and  the  forces  accurate,  it  is 
quite  possible  to  consume  more  than  a  reasonable  amount  of  time. 
Again,  it  is  not  always  easy,  and  frequently  impossible,  to  deter- 
mine exactly  the  forces  acting  on  a  given  piece.  But  their  nature, 
whether  sudden  or  slowly  applied,  rapid  in  action  or  only  oc- 
curring at  intervals,  and  their  approximate  direction  and  magni- 
tude at  least,  are  always  capable  of  analysis.  There  are  few,  if 
any,  cases  where  close  assumptions  cannot  be  made  on  the  &bove 
basis  and  the  design  proceeded  with  accordingly.  Hence  the 
danger  of  too  great  refinement  of  analysis  is  simply  to  be  avoided 
by  the  designer's  plain  business  sense. 

The  first  tendency  of  the  student  is  to  pass  over  the  study  of 
the  forces  as  dull  and  dry,  and  attempt  the  design  at  once.  He 
soon  finds  himself  facing  problems  oi  which  he  sees  no  possible 
solution,  and  he  bases  his  design  on  pure  guess-work.  This  is 
the  only  solution  possible  from  such  a  point  of  view,  and  is  really 
no  solution  at  all.  A  guer.s  which  has  some  rational  backing  is 
often  successful;  but  in  that  case  some  analysis  is  required,  and  it 
is  not  a  pure  guess,  but  falls  under  the  very  principle  we  are 
considering. 

There  is  no  short  cut  to  the  design  of  machine  parts  which 
avoids  this  full  understanding  of  the  forces  that  they  must 
sustain.  The  size  of  a  belt  depends  upon  the  maximum  pull 
upon  it,  and  the  designing  of  belts  is  nothing  but  providing 
sufficient  cross-section  of  leather  to  prevent  the  belt  tearing  under 


19 


12  MACHINE 


the  pull.  Again,  if  pulley  arms  are  not  to  break,  or  shafts  twist 
oil",  or  bolts  be  torn  apart,  or  the  teeth  of  gears  fail,  or  keys  and 
pins  shear  ofr,  we  must  first,  of  course,  iind  out  what  .forces  exist 
which  are  likely  to  produce  stress  that  may  lead  to  such 
breakage.  "We  should  not  guess  at  the  sizes,  and  then  run  the 
machine  to  see  if  breakage  results,  and  then  guess  again.  Ma- 
chines are  sometimes  built  in  this  way,  but  it  is  an  unreasonable 
and  uncertain  method.  We  must  use  every  effort  to  foresee  the 
stress  which  a  piece  ia  liable  to  receive,  before  we  decide  its  size, 
"We  must  know  all  the  forces  approximately,  if  not  positively. 
The  analysis  must  be  thorough  enough  to  permit  of  reasonable 
assumption,  if  not  positive  assertion,  it  ia  manifestly  impossible 
to  solve  any  problem  until  we  know  exactly  what  the  problem  is; 
and  a  full  analysis  is  the  statement  of  the  problem. 

2.  Theoretical  Design.  After  we  know  by  careful  analysis 
what  stress  the  machine  part  has  to  sustain,  the  next  step  is  so  to 
design  it  that  it  will  theoretically  resist  the  applied  forces  with 
the  least  expenditure  of  material. 

"We  often  see  machinery  with  the  metal  of  which  it  is  made 
distributed  in  the  worst  possible  manner.  In  places  where  the 
stress  is  heavy  and  a  rigid  member  is  needed,  we  find  a  weak, 
springy  part;  wrile  in  other  parts,  where  there  are  no  forces  to  be 
resisted,  or  vibration  to  be  absorbed,  there  seems  to  be  a  waste  of 
good  material.  Whether  in  such  case  the  analysis  of  the  forces 
was  poor,  or  perhaps  not  made  at  all,  or  whether  a  knowledge  of 
how  to  design  so  as  to  resist  the  given  forces  was  wholly  absent, 
cannot  be  told.  At  any  rate,  lack  of  either  or  both  is  clearly 
shown  in  the  result. 

Any  member  of  a  machine  may  vary  in  form  from  a  solid 
block  or  chunk  of  material  to  an  open  ribbed  structure.  The  solid 
chunk  fills  the  requirement  as-faras  strength  is  concerned,  unless 
it  is  so  heavy  as  to  fail  from  its  own  weight.  But  such  construe- 
tion  is  poor  design,  except  in  cases  where  the  concentration  of 
heavy  mass  <s  necessary  to  absorb  repeated  blows  like  those  of  a 
hammer.  The  possibility  of  these  blows  should,  however,  have 
been  determined  in  the  analysis;  and  the  solid,  anvil  construction 
then  becomes  theoretical  design  for  that  analysis. 

For  steadily  applied  loads  an  open,  ribbed,  or  hollow  box 


. 


MACHINE  DESIGN  13 

structure  can  be  made  which  will  distribute  the  metal  where  it  is 
theoretically  needed,  and  each  fiber  will  then  sustain  its  proper 
share  of  the  load.  In  this  way  weight,  cost,  and  appearance  are 
heeded;  and  the  service  of  the  piece  is  as  good  as,  and  probably 
better  than,  it  would  be  with  the  clumsy,  solid  form. 

There  is  no  such  thing  as  putting  too  much  theory  into  the 
design  of  machinery.  The  strongest  trait  which  an  engineer  can 
have  is  absolute  faith  in  his  analyses  and  calculations,  and  their 
reproduction  in  hia  theoretical  design.  Theoretical  design  is  an 
indication  of  scientific  advance  in  the  art,  and  some  of  the  greatest 
steps  of  progress  which  have  been  made  in  recent  years  have  been 
accomplished  through  a  purely  theoretical  study  of  machine 
structure. 

It  will  never  do,  however,  to  be  satisfied  with  theoretical 
design  when  it  is  not  in  accord  with  modern  commercial  and  manu- 
facturing considerations.  Hence  the  next  step  after  the  determina- 
tion of  the  theoretical  design  is  the  study  of  it  from  the  producing 
standpoint. 

3.  Practical  Modification.  All  theoretical  design  viewed  from 
the  business  standpoint  is  worthless,  unless  it  has  been  subjected 
to  the  test  of  cheap  and  efficient  production.  Each  machine  detail, 
though  correct  in  theory,  may  yet  be  improperly  shaped  and  unfit 
for  the  part  it  is  to  play  in  the  general  scheme  of  manufacture. 

The  conditions  here  involved  are  changeable.  What  is  good 
design  in  this  decade  may  be  bad  in  the  next.  In  this  light  the 
designer  must  be  a  close  student  of  the  signs  of  the  times ;  he  must 
follow  the  march  of  progress,  closely  applying  existing  resources, 
conditions,  and  facilities,  otherwise  he  cannot  produce  up-to-date 
designs.  The  introduction  of  new  raw  materials,  the  cheapening 
of  production  of  others,  the  changing  of  shop  methods,  tha  use  of 
special  machinery,  the  opening  of  new  markets,  the  development 
of  new  motive  agents,  —  all  these  and  many  others  are  constantly 
demanding  some  modification  in  design  to  meet  competition. 

Illustrative  of  this,  note  the  change  which  has  been  wrought 
by  the  development  of  electric  power,  the  rise  and  decline  of  the 
bicycle  business,  the  present  manufacture  of  automobiles,  the  last 
named  especially  with  reference  to  the  development  of  the  small 
motive  unit,  the  gasolene  engine,  the  steam  engine,  etc.  The 


It  MACHINE  DESIGN 

design  of  much  machinery  has  been  materially  changed  to  meet 
the  exacting  demands  of  these  new  enterprises. 

Practical  modifications  of  design  necessary  to  meet  the  limi. 
tations  of  construction  in  the  pattern  shop,,  foundry,  and  machine 
shop  :;re  of  daily  application  in  the  designer's  work.  He  must 
keep  i!,  his  mind's  eye  at  all  times  the  workmen  and  the  processes 
tK-y  use  to  create  his  designs  in  metal  in  the  shop. 

"How  can  this  be  made?"  "Can  it  be  made  at  all?" 
"Can  it  be  made  cheaply?"  ""Will  it  be  simple  in  operation 
after  it  is  made"""  "Can  it  be  readily  removed  for  repair?" 
"  Can  it  be  lubricated  ?  "  "  How  can  it  be  put  in  place  ?  "  "  How 
can  it  be  gotten  out?"  "Will  it  be  made  in  small  quantities 
qr  laro-e?"  "Will  it  sell  as  a  special  or  standard  machine?" 
etc.,  etc. 

The  consideration  of  such  questions  as  these  is  a  practical 
necessity  as  a  business  matter.  Xo  other  feature  affects  the 
design  of  machinery  more,  perhaps;  for  designs  which  cannot  be 
built  as  business  propositions  are  no  designs  at  all. 

The  student,  it  is  true,  may  not  have  the  extended  shop 
knowledge  which  is  essential  to  this;  but  he  cuu  do  much  for 
himselt  by  visiting  shops  whenever  possible,  getting  hold  of  shop 
ways  of  doing  things,  and  invariably  treating  his  work  as  a 
business  matter.  Though  a  man  may  not  be  a  pattern  maker, 
molder,  blacksmith,  or  machinist,  yet  he  can  soon  gain  ideas  o*  the 
processes  in  each  of  these  branches  which  \vill  be  of  immense 
advantage  to  him  in  his  designing  work. 

4.  Delineation  and  Specification.  This  means  the  clear  and 
concise  representation  of  the  design  by  mechanical  drawings. 

This  is  as  much  a  part  of  the  routine  method  of  Machine  De- 
sign'as  the  other  three  points  which  have  been  discussed.  The 
mere  act  of  putting  the  results  of  mechanical  thinkino-  on  paper  is 
one  of  the  greatest  helps  to  force  thinking  machinery  to  system- 
atic and  definite  action.  A  designer  never  thinks  very  long 
without  drawing  something,  and  the  student  must  bring  himself  to 
feel  that  a  drawing  in  its  tirst  sense  is  a  means  of  helping  hit*  owrj 
thought,  and  must  freely  use  it  as  such. 

In  its  second  and  final  sense,  the  drawing  is  an  order  and 
specification  sheet  from  the  designer  to  the  work: nan.  Design 


MACniJSTE  DESIGN  15 

which  stops  short  of  exact,  finished  delineation  in  the  form  of 
working  shop  drawings  is  only  half  done.  In  fact  the  possibility 
of  a  piece  being  thus  exactly  drawn  is  often  the  crucial  test  of  its 
feasibility  as  a  part  of  a  machine.  It  is  easy  to  make  general  out- 
lines, but  it  is  not  so  easy  to  get  down  to  finished  detail.  It  is 
safe  to  say  that  there  is  no  one  thing  productive  of  more  trouble, 
delay  and  embarrassment,  and  waste  of  time  and  money  in  the 
shop,  when  there  need  be  none  from  this  cause,  than  a  poor  detail 
drawing.  The  efficiency  of  the  process  of  design  is  not  fully  real- 
ized, and  failures  are  often  recorded  where  there  should  be  success, 
merely  because  the  indefiniteness  permitted  by  the  designer  in  the 
drawings  naturally  transmitted  itself  to  the  workman,  and  he  in 
turn  produced  a  part  indefinite  in  form  and  operation. 

The  actual  process  of  drawing  in  the  development  of  a  design 
may  be  outlined  as  follows  : 

Rough  sketches  merely  representing  ideas,  not  drawn  to  scale, 
are  first  made.  These  are  of  use  only  so  far  as  the  choice  of  me- 
chanical ideas  is  concerned,  and  to  carry  preliminary  dimensions. 

Following  these  sketches,  comes  a  layout  to  scale,  of  the 
favored  sketch,  a  working  out  of  the  relative  sizes  and  location  of 
the  parts.  This  drawing  may  be  of  a  sketchy  nature,  carrying  a 
principal  dimension  here  and  there  to  fix  and  control  the  detailed 
design.  In  this  drawing  the  design  is  developed  and  general  detail 
worked  out.  The  minute  detail  of  the  individual  parts  is,  however, 
left  to  the  subsequent  working  drawing. 

This  layout  drawing  may  now  be  turned  over  to  an  expert 
draftsman  or  detail  designer,  who  picks  out  each  part,  makes  an 
exact  drawing  of  it,  studying  every  little  detail  of  its  shape,  *nd 
finally  adds  complete  dimensions  and  specifications  so  that  the 
workman  is  positively  informed  as  to  every  point  of  its  construction. 
..  General  drawings  and  cross  sections  constitute  the  last  step 
in  the  process  of  complete  delineation.  These  show  the  parts 
assembled  in  the  complete  machine.  They  also  serve  a  valuable 
purpose  to  the  draftsman  in  checking  up  the  dimensions  of  the 
detail  drawings.  Errors  which  have  escaped  previous  notice  are 
often  discovered  in  this  way.  The  layout,  mentioned  above,  is 
sometimes  finished  up  into  a  general  drawing;  but  it  is  safer  to 
make  an  entirely  new  drawing,  as  changes  in  detail  are  often 
necessary  after  the  layout  is  made. 


:23 


16  MACHINE  DESIGN 


The  four  fundamental  lines  of  thought  and  action  noted 
above  may  be  summarized  thus — "analyse  and  theorize,  modify 
and  delineate."  This  is  a  maxim  easy  to  remember,  applicable 
to  every  problem  in  Machine  Design,  and  always  provides  the 
ans\\er  to  the  question  "What  shall  I  do,  how  shall  I  proceed?" 
by  pointing  out  the  proper  sequence  in  the  course  to  be  followed. 

CONSTRUCTIVE    MECHANICS. 

Mechanics  is  a  constructive  science,  its  principles  lying  at  the 
root  of  the  design  and  operation  of  all  machinery.  It  is  usually 
taught,  however,  as  an  advanced  mathematical  subject;  and  the 
student  gets  his  original  conceptions  of  forces,  moments,  and 
beams  in  the  abstract,  before  he  realizes  the  constructive  value  of 
such  conceptions.  By  "Constructive  Mechanics"  is  meant  the 
study  of  a  machine  purely  from  its  constructive  side,  the  viewing 
of  the  parts  with  respect  to  their  "mechanics,"  and  satisfying  the 
requirements  of  the  same  in  form  and  arrangement. 

The  student  may  cultivate  this  habit  of  clear,  mechanical  per- 
ception by  constantly  noting  the  "  mechanics "  of  the  simple 
structures  which  he  sees  in  his  daily  routine  of  work.  Aside 
from  machinery,  in  which  the  "mechanics"  is  often  obscure, 
the  world  is  full  of  simple  examples  of  natural  strength  and 
symmetry,  explainable  by  application  of  the  principles  of  pure 
"mechanics." 

Posts  and  pillars  are  largest  at  their  bases;  overhanging 
brackets  or  arms  are  spread  out  at  the  fastening  to  the  wall; 
heavy  swinging  gates  are  counter-balanced  bv  a  ponderous  weight; 
the  old-fashioned  well  sweep  carries  its  tray  of  stones  at  the  end, 
adjusting  the  balance  to  a  nicety;  these  are  examples  of  things 
depending  for  their  form  and  operation  upon  the  principles  of 
'•mechanics."  The  building  of  them  involved  "constructive 
mechanics,"  and  yet  their  constructor  perhaps  never  heard  of  the 
science,  using  merely  his  natural  sense  of  mechanical  fitness 
Such  simple  reasoning  is,  however,  Constructive  Mechanics. 

Forces,  Moments,  and  Beams.     Machines  are  nothino-  but  a, 

O 

collection  of  (1)  parts  taking  direct  stress,  or  (2)  parts  acting  as 
loaded  beams.  Forces  actino*  iritJiout  leverage  produce  direct 
stress  ou  the  sustaining  part.  Forces  acting  with  leverage  pro- 


MACHINE  DESIGN  17 

duce  a  moment;  the  sustaining  member  is  a  beam,  and  the  stress 
therein  depends  on  the  theory  of  beams,  as  explained  in  "  Me- 
chanics." 

An  example  of  the  first  fs  the  load  on  a  rope,  the  force  acting 
without  leverage,  and  the  rope  therefore  having  a  direct  stress  put 
upon  it. 

An  example  of  the  second  is  a  push  of  the  hand  on  the  crank 
of  a  grindstone.  A  moment  is  produced  about  the  hub  of  tho 
crank;  the  arm  of  the  crank  is  a  beam,  and  the  stress  at  any  point 
of  it  may  be  found  by  the  method  of  theory  of  beams. 

Tension,  Compression,  and  Torsion.  The  stress  induced  in 
the  sustaining  part,  whether  tensile,  compressive,  or  torsional,  is 
caused  by  the  application  of  forces,  either  acting  directly  without 
leverage,  o^  with  leverage  in  the  production  of  moments. 

The  forces  applied  from  external  sources  are  at  constant  war 
with  the  resisting  forces  due  to  the  strength  of  the  fibres  of  the 
material  composing  the  machine  members.  The  moments  of  the 
external  forces  are  constantly  exerted  against  and  balanced  by  the 
moments  of  the  internal  resistance  of  the  material.  Hence, 
design,  from  a  strength  standpoint,  is  merely  a  balancing  of 
internal  strength  against  external  force.  In  other  words,  we  may 
in  all  cases  write  a  sign  of  equality,  place  the  applied  effort  on 
one  side,  the  effective  resistance  on  the  other,  and  we  shall  have 
an  equation,  which,  if  capable  of  solution,  will  give  the  proper 
proportions  of  the  parts  considered. 

External  Force  =  Internal  Resistance. 
External  Moment  =  Internal  Moment  of  Resistance. 
Expressed  in  terms  of  the  "  Mechanics:" 
P=AS          (i) 

BorT=E.          (a) 

In  these  formulas,  which  are  perfectly  general, 

P=dircct  load  in  pounds. 

A=area  of  effective  material,  in  square  inches. 

S=working  fibre  stress  of  the  material  (tensile,  compressive,  or  shear- 
ing), in  pounds  per  square  inch. 

8  or  T=external  moment  (bending  or  torsional),  in  inch-pounds. 

I=moment  of  inertia  (direct  or  polar),  of  the  resisting  section. 

c= distance  of  the  most  remote  fibre  of  the  resisting  section  from  the 
neutral  axis. 


IS  MACHINE  DESIGN 

P  may  produce  direct  tensile,  compressive,  or  shearing  stress. 

B  may  produce  tensile  or  compressive  stress,  and  requires  use  of  direct 
moment  of  inertia  in  either  case. 

T  produces  shearing  stress,  and  requires  use  of  polar  moment  of 
inertia. 

The  origin  of  formula  (1)  is  obvious,  the  assumption  being 
that  the  fibre  stress  is  equally  distributed  to  every  particle  in  the 
area  "A." 

The  development  of  formula  (2)  is  given  in  any  text-book  in 
Mechanics.  It  requires  the  aid  of  the  Calculus,  however.  Any 
good  handbook  gives  values  for  both  the  direct  moment  of  inertia 
and  the  polar  moment  of  inertia  for  quite  a  large  variety  of  sections, 
so  that  further  reference  is  an  easy  matter  for  the  student.  These 
rallies  are  also  obtained  through  the  methods  of  the  Calculus. 

The  reason  for  introducing  these  formulas  at  this  time  is  to 
call  the  attention  of  the  student  especially  to  the  fact  of  their 
universal  and  fundamental  use  in  all  problems  concerning  the 
strength  of  machine  parts.  Nearly  every  computation  may  be 
reduced  to  or  expanded  from  these  two  simple  equations.  .Many 
complex  combinations  occur,  of  course,  which  will  not  permit  sim- 
ple and  direct  application  of  these  formulas,  but  the  student  will 
do  well  to  place  himself  in  perfect  command  of  these  two.  Assuming 
that  he  is  able  to  analyze  forces,  and  compute  the  simple  moment 
at  the  point  where  he  wishes  to  find  the  strength  of  section,  the 
rest  is  the  mere  insertion  of  the  assumed  working  fibre  stress  of 
the  material  in  the  formula  (2)  above,  and  solution  for  the  quantity 
desired. 

When  the  case  is  one  of  combined  stress,  the  relation  becomes 
more  complicated  and  difficult  of  analysis  and  solution.  The  most 
common  case  is  where  bending  is  combined  with  torsion,  as  in  the 
case  of  a  shaft  transmitting  power,  and  at  the  same  time  loaded 
transversely  between  bearings.  In  fact  there  are  very  few  cases  of 
shafts  in  machines,  which,  at  some  part  of  their  length,  do  not 
hav;;  tliis  combined  stress.  In  this  case  the  method  of  procedure 
is  to  find  the  simple  bending  moment  and  the  simple  torsional 
moment  separately,  in  the  ordinary  way.  Then  the  theory  of 
elasticity  furnishes  us  with  a  formula  for  an  equivalent  bending 
or  an  equivalent  torsional  moment  which  is  supposed  to  produce 
tee  same  effect  upon  the  fibres  of.  the  material  as  the  combined 


2  ; 


21-INCH  SLOTTING  MACHINE. 


MACHINE  DESIGN 


action  of  the  two  simple  moments  acting  together.  In  other 
words,  the  separate  moments  combined  in  action,  being  impossible 
of  solution  in  that  form,  are  reduced  to  an  equivalent  simple 
moment  and  the  solution  then  becomes  the  same  as  for  the  prev- 
ious case. 

These  equivalent  equations  are  given  below,  the  subscript  "e" 
being  added  to  express  separation  from  the  simple  moment: 

(3) 

(4) 

Be  and  Te,  found  from  these  equations,  are  the  external  mo- 
ments, and  are  to  be  equated  to  the  internal  moments  of  resistance 
of  the  section  precisely  as  if  they  were  simple  bending  or  torsional 
moments.  Either  may  be  used.  For  shafts  (4)  is  generally  used, 
being  the  simpler  of  the  two  in  form. 

FRICTION   AND   LUBRICATION. 

The  parts  of  a  machine  which  have  no  relative  motion  with 
regard  to  each  other  are  not  -dependent  upon  lubrication  of  their 
surfaces  for  the  proper  performance  of  their  functions.  In  cases 
where  relative  motion  does  occur,  as  between  a  planer  bed  and  its 
ways,  a  shaft  and  its  bearing,  or  a  driving  screw  and  its  nut, 
friction,  and  consequent  resistance  to  motion,  will  inevitably 
occur.  Heat  will  be  generated,  and  cutting  or  scoring  of  the 
surfaces  will  take  place  if  the  surfaces  are  allowed  to  run  together 
dry. 

This  difficulty,  which  exists  with  all  materials,  cannot  be 
overcome,  for  it  is  a  result  of  roughness  of  surface,  characteristic 
of  the  material  even  when  highly  finished.  The  problem  of  the 
designer,  then,  is  to  take  conditions  as  he  finds  them,  and,  as  he 
cannot  change  the  physical  characteristics  of  materials,  so  choose 
those  which  are  to  rub  together  in  the  operation  of  the  machine 
that  friction  will  be  reduced  to  the  lowest  possible  limit.  Now  it 
fortunately  happens  that  there  are  certain  agents  like  oil  and 
graphite,  wrhich  seem  to  fill  up  the  hollows  in  the  surface  of  a 
solid  material,  and  which  themselves  have  very  little  friction  on 
other  substances.  Hence,  if  a  machine  permits  by  its  design  an 
automatic  supply  of  these  lubricating  agents  to  all  surfaces  having 


27 


MACHINE  DESIGX 


motion  between  them,  friction  may  be  reduced  to  the  lowest  limit. 

If  this  full  supply  of  lubricant  be  secured,  and  the  parts  still 
heat  and  cut,  then  the  fault  may  be  traced  to  other  causes,  such  as 
springy  surfaces,  localization  of  pressure,  or  insufficient  radiating 
surface  to  carry  away  the  heat  of  friction  as  fast  as  it  is  generated. 

Lubricating  agents  are  of  a  nature  running  from  the  solid 
graphite  form  to  a  thick  grease,  then  to  a  heavy  dark  oil,  and 
finally  to  a  thin,  fluid  oil  flowing  as  freely  as  water.  The  solid  and 
heavy  lubricants  are  applicable  to  heavily  loaded  places  where  the 
pressure  would  squeeze  out  the  lighter  oils.  Grease,  forced  be- 
tween the  surfaces  by  compression  grease  cups,  is  an  admirable 
lubricator  for  heavy  machinery  under  severe  service.  High-speed 
and  accurate  machinery,  lightly  loaded,  requires  a  thin  oil,  as  the 
fits  would  not  allow  room  for  the  heavier  lubricants  to  find  their 
way  to  the  desired  spot.  The  ideal  condition  in  any  case  is  to 
have  a  film  of  lubricant  always  between  the  surfaces  in  contact, 
and  it  is  this  condition  at  which  the  designer  is  always  aiming  in 
his  lubricating  devices. 

Oil  ways  and  channels  should  be  direct,  ample  in  size. 
readily  accessible  for  cleaning,  and  distributing  the  oil  by  natural 
ilo\vr  over  the  full  extent  of  the  surface.  Hidden  and  remote 
bearings  must  be  reached  by  pipes,  the  mouths  of  which  should 
bo  clearly  indicated  and  accessible  to  the  operator  of  the  machine. 
Such  pipes  must  be  straight,  if  possible,  and  readily  cleaned. 

There  is  one  practical  principle  affecting  the  design  of 
methods  of  lubrication  of  a  machine  which  should  be  borne  in 
mind.  This  is,  "Neglect  and  carelessness  by  the  operator  ynmst 
be  provided  for."  It  is  of  no  use  to  say  that  the  ruination  of  a 
surface  or  hidden  bearing  is  due  to  neglect  by  the  operator,  if  the 
means  for  such  -lubrication  are  not  perfectly  obvious.  This  is 
"  locking  the  door  after  the  horse  is  stolen."  The  designer  has 
not  done  his  duty  until  he  has  made  the  scheme  of  lubrication  so 
plain  that  every  part  'must  receive  its  proper  supply  of  oil,  except 
by  gross  and  willful  negligence,  for  which  there  can  be  no 
possible  just  excuse. 

WORKING    STRESSES   AND   STRAINS. 

Some  persons  object  to  the  use  of  these  terms,  as  one  is 
fraquently  used  for  the  other,  and  misunderstanding  results.  Tins 


28 


MACHINE  DESIGN  21 

is  doubtless  true;  but  the  student  may  as  well  learn  the  true 
relation  of  the  terms  once  for  all,  because  he  will  frequently  run 
across  them  in  his  reading  and  reference  work,  and  should  inter- 
pret them  rightly.  The  strict  relation  of  the  two  is  as  follows: 

Stress  is  the  internal  force  in  a  piece  resisting  the  external 
force  applied  to  it.  A  weight  of  ten  pounds  hanging  on  a  rope 
produces  a  stress  of  ten  pounds  in  the  rope. 

Strain  is  the  change  of  shape,  or  deformation,  in  a  piece 
resisting  an  external  force  applied  to  it.  If  the  above  weight  of 
ten  pounds  stretches  the  rope  J  inch,  the  strain  is  J  inch. 

Unit  stress  is  stress  per  unit  area,  e.  g.,  per  square  inch. 

Unit  strain  is  strain  per  unit  length,  e.  g,,  per  inch  length. 

In  the  above  case,  if  the  rope  were  -|  square  inch  in  area 
and  30  inches  long,  the  unit  stress,  or  intensity  of  stress,  is 
10-7-1 1=20  pounds  per  square  inch;  the  unit  strain  is  J-=-80=T|ir 
inch  per  inch. 

"When  stress  is  induced  in  a  piece,  the  strain  is  practically 
proportional  to  the  stress  for  all  values  of  the  stress  below  the 
elastic  limit  of  the  material;  and  when  the  external  load  is  re- 
moved the  strain  will  entirely  disappear,  or  the  recovering  power 
of  the  material  will  restore  the  piece  to  the  original  length. 

Illustrating  by  the  case  above,  on  the  supposition  that  the 
elastic  limit  has  not  been  reached  by  the  stress  of  20  pounds  per 
square  inch,  if  the  load  of  10  pounds  were  taken  off,  the  J-inch 
strain  would  disappear  and  the  rope  return  to  its  original  length; 
if  the  load  were  changed  to  -|  of  10  pounds,  or  5  pounds,  the 
strain  would  be  i  of  J  inch,  or  J  inch. 

Now  it  is  found  that  if  we  wish  a  piece  to  last  in  service  for 
a  long  time  without  danger  of  breakage,  we  must  not  permit  it 
to  be  stressed  anywhere  near  the  elastic  limit  value.  If  we  do, 
although  it  will  probably  not  break  at  once,  it  is  in  a  dangerous 
condition,  and  not  well  suited  to  its  requirements  as  a  machine 
member.  The  technical  name  for  this  weakening  effect  is  "  fa. 
tigue."  It  is  further  found  that  the  fatigue  due  to  this  repeated 
stress  is  reached  at  a  lower  limit  when  the  stress  is  alternating  in 
character  than  when  it  is  not.  In  other  words,  if  we  first  pull  on 
a  piece  and  then  push  on  it,  we  shall  first  have  the  piece  in  tension 
and  theu  in  compression;  this  alternation  of  stress  repeated  to 


22  MACHINE  DESIGN 

near  the  elastic  limit  of  the  material  will  fatigue  it,  or  wear  out 
the  fibres,  and  it  will  finally  fail.  If,  however,  we  first  pull  on 
the  piece  with  the  same  force  as  before,  and  then  let  go,  we  shall 
first  have  the  piece  in  tension  and  then  entirely  relieved;  such 
repetition  of  stress  will  finally  "  fatigue  "  the  material,  but  not  so 
quickly  as  in  the  first  case.  Experiments  indicate  that  it  may 
take  twice  as  many  applications  in  the  latter  case  as  in  the  former. 

The  working  stress  of  materials  permissible  in  machines  is 
based  on  the  above  facts.  The  breaking  strength  divided  by  a 
liberal  factor  of  safety  will  not  necessarily  give  a  desirable  work- 
ing stress.  The  question  to  be  answered  is,  "^V  ill  the  assumed 
working  fibre  stress  permit  an  indefinite  number  of  applications 
of  the  load  without  fatiguing  the  material  ? " 

Hence  we  see  that  the  same  material  may  be  safely  used  under 
different  assumptions  of  working  stress.  For  example,  a  rotating 
shaft,  heavily  loaded  between  bearings,  acts  as  a  beam  which  in 
each  revolution  is  having  its  particles  btibjected,  first  to  a  maxi- 
mum tensile  stress,  and  then  to  a  maximum  compressivo  stress. 
This  is  obviously  a  very  different  stress  from  that  which  the  same 
piece  would  receive  if  it  were  a  pin  in  a  bridge  truss.  In  the 
former  we  have  a  case  where  the  stress  on  each  particle  reverses  at 
each  revolution,  while  in  the  latter  wo  have  merely  the  same  stress 
recurring  at  intervals,  but  never  becoming  of  the  opposite  char- 
acter. For  ordinary  steel,  a  value  of  8,000  would  be  reasonable  in 
the  former  case,  while  in  the  latter  it  may  be  much  higher  with 
safety,  perhaps  nearly  double. 

From  the  facts  stated  above,  it  is  evident  that  exact  values  for 
working  fibre  stress  cannot  be  assumed  with  certainty  and  applied 
broadly  in  all  cases.  If  the  elastic  limit  of  the  material  is  defi- 
nitely known  we  can  base  our  working  value  quite  surely  on  that. 

"With  but  a  general  knowledge  of  the  elastic  limit,  ordinary 
steel  is  good  for  from  12,000  to  15,000  pounds  per  square  inch 
non -reversing  stress,  and  8.000  to  10,000  reversing  sfress.  Cast 
iron  is  such  an  uncertain  metal  on  account  of  its  variable  structure 
that  stresses  are  always  kept  low,  say  from  3,000  to  4,000  for  non- 
reversing  stress,  and  1,500  to  2,500  for  reversing  stress. 

"With  these  values  as  a  guide,  and  the  special  conditions  con. 
trolling  each  case  carefully  studied,  reasonable  limits  may  be 


30 


-•*/ 

$• 

i^J 


/Borrow  PLATES 

SEMI-CIRCULAR  3'-o"f?/to. 

^  RECfD 


12  "X  96 "  ACCUMUL  A  TOR 
SCALE:-I"J±  ",3'=lFT 


HYDRAULIC  ACCUMULATOR 
Detail  Drawing,  to  be  used  with  Figure  on  Opposite  PAg€ 


HYDRAULIC  ACCUMULATOR 

Assenjblea  Drawing  with  Petals  op  the  §£vme  Sbf§t 


MACHINE  DESIGN  23 

assigned  for  working  stress,  not  only  of  steels,  various  grades  of 
cast  iron,  and  mixtures  of  the  same,  but  of  other  alloys,  brass, 
bronze,  etc.  Gun  metal,  semi-steel,  and  bronze  are  intermediate 
in  strength  between  cast  iron  and  steel.  Data  on  the  strength  of 
materials  are  available  in  any  of  the  handbooks,  and  should  be  con- 
sulted freely  by  the  student.  They  will  be  found  somewhat  con- 
flicting, but  will  assist  the  judgment  in  coming  to  a  conclusion. 

Application  to  Practical  Case.  In  actual  practice  the  only 
information  which  the  designer  has,  upon  which  to  base  his  design, 
is  the  object  to  be  accomplished..  He  must  choose  or  originate 
suitable  devices,  develop  the  arrangement  of  the  parts,  make  his 
own  assumptions  regarding  the  operation  of  the  machine,  then 
Analyse  and  Theorize,  Modify  and  Delineate  each  detail  as 
he  meets  it. 

This,  it  Will  be  found,  is  a  very  different  matter  from  taking 
some  familiar  piece  of  machinery,  such  as  a  pulley,  or  a  shaft,  or 
a  gear,  as  an  isolated  case,  the  load  being  definitely  given,  and 
proceeding  with  the  design.  This  is  easily  done,  but  is  only  half 
the  problem,  for  machine  parts,  such  as  pulleys,  gears,  and  shafts, 
do  not  confront  the  designer  tagged  or  labeled  with  the  conditions 
they  are  to  meet.  He  is  to  provide  parts  to  meet  the  specific,  con- 
ditions,  and  it  is  as  much  a  part  of  his  designing  method  to  know 
how  to  attack  the  design  of  a  machine  as  it  is  to  know  how  to 
design  the  parts  in  detail  after  the  attack  has  reduced  the  members 
to  definitely  loaded  structures.  The  whole  process  must  be  gone 
through,  the  preliminary  sketches,  calculations,  and  layout,  all  of 
which  precede  the  detail  design  and  working  drawings;  and  no  step 
of  the  process  can  be  omitted. 

It  is  for  this  reason  that  the  present  case  used  for  illustration 
is  carried  out  quite  thoroughly.  The  student  should  make  himself 
familiar  with  every  step  of  the  designing  method  as  applied  to  this 
simple  case  of  design.  More  complex  problems,  handled  in  the 
same  way,  will  simplify  themselves;  and  when  the  point  is  reached 
where  confidence  exists  to  take  hold  of  the  design  of  any  machine, 
however  unfamiliar  its  object  may  be,  or  however  involved  its 
probable  detail  appears,  the  student  has  become  the  true  designer. 
It  ia  the  knowing  how  to  attack  a  problem,  to  start  definite  work 
on  it,  to  go  ahead  boldly,  confident  that  the  method  applied  will 


MACHINE  DESIGN 


produce  results,  that  giv°3  command  of  the  design  of  machinery 
and  wins  engineering  success. 


The  special  case  which   has    been  chosen   to  illustrate  the 
application  of  the  principles  stated  in  the  foregoing  pages  is  ideal, 


MACHINE  DESIGN 


in  that  it  does  not  represent  any  actual  machine  at  present  in 
operation.  Probably  builders  of  hoisting  machinery  have  devices 
which  would  improve  the  machine  as  shown.  In  detail,  as  well 
as  arrangement,  they  could  doubtless  make  criticism  as  manufac- 
turers. The  arrangement  as  shown  is  merely  intended  to  bring 
out  in  simplest  form  the  common  elements  of  transmission  ma- 
chinery  as  parts  of  some  definite  machine,  instead  of  as  isolated 
details.  The  design  is  one  entirely  possible,  practical,  and  me- 
chanical, but  special  attention  has  been  paid  to  simplicity  in  order 
to  enable  the  student  to  follow  the  method  closely,  for  the  method 
is  the  chief  thing  for  him  to  acquire. 

The  student  is  expected  to  refer  constantly  to  Part  II  for  a 
more  formal  and  general  discussion  of  the  simple  machine  ele- 
ments involved  in  the  case  considered.  Part  II  is  intended  to  be 
a  simplified  and  condensed  reference  book,  carried  out  in  accord- 
ance with  the  method  of  machine  design  as  specified  in  Part  I. 
The  student  should  not  wait  until  he  has  completed  the  study  of 
this  part  before  taking  up  Part  II,  for  the  latter  is  intended  for 
use  with  the  former  in  the  solution  of  the  problems. 

In  the  case  of  power  transmission  about  to  be  studied,  the 
running,  conversational  method  employed  assumes  that  the  student 
is  in  possession  of  the  matter  in  Part  II  on  the  subject  considered. 
Thus,  in  the  design  of  the  pulley,  reference  to  the  subject  of 
"  Pulleys  "  in  Part  II  is  necessary  to  follow  the  train  of  calcula- 
tion; in  designing  the  gear,  consult  "Gears;"  in  calculating  size 
of  shafts,  see  «  Shafts,"  etc.,  etc. 

Problem.     A  machine  is  to  be  designed  to  be  set  on  the  floor 
of  a  building  to  drive  a  wire  rope  falling  from  the  overhead 
sheaves  of  an  elevator  or  hoist.     Without  regard  to  details  of  this 
overhead  arrangement,  for  its  design  would  be  a  separate  problem, 
suppose  that  the  data  for  the  rope  are  as  follows: 

Load  on  rope.  .  .  ...............  ----  5,000  pounds. 

Speed  of  rope  .....................   150  feet  per  minute. 

Length  of  rope  to  be  reeled  in  ......    200  feet. 

We  shall  further  assume  that  the  driving  power  is  to  be  an 
electric  motor  belted  to  the  machino,  that  the  required  speed 
reduction  can  be  satisfactorily  obtained  by  a  single  pair  of  pulleys 
and  one  pair  of  gears,  and  that  a  plain  band  brake  is  to  be  applied 
to  the  drum. 


37 


MACHINE  DESIGN 


TVith  this  data  we  shall  proceed  to  work  out  the  detail  design 
of  the  machine. 

Preliminary  Sketch.  The  first  thing  to  do  is  to  sketch 
roughly  the  proposed  arrangement  of  the  machine. 

This  might  appear  like  Fig.  1  except  that  it  would  have  no 
dimensions  in  addition  to  the  data  given  above.  If  the  scheme 
seems  suitable,  the  next  step  is  to  make  such  preliminary  calcula- 
tions as  will  give  further  data,  exact  or  closely  approximate  sizes, 
to  be  put  at  once  on  the  sketch,  to  outline  the  future  design. 

Rope  and  Drum.     Referring  to  tables  of  strength  of  wire  rope 
(Kent's  Pocket  Book  gives  the  manufacturers'  list),  we  find  that 
a  £-inch  cast-steel  rope  will  carry  5,000  pounds  safely,  and  that  the 
proper   si/e  of   drum   to  avoid 
excessive    bending  of    the  rope 
around  it  is  27  inches  diameter. 
Allowing  J-  inch  between   the 
coils  is  the   rope  winds  on  the 
drum,  the  pitch  of  coil  will  be 
:[  inch  as  shown  in  SKetch,  Fig. 
3.     The  length  of  one  complete 

27  X  3.1410 
coil  is,  practically,  —  — 17; — 


Fig.  2. 
200 


—7.07  feet.    To  provide  for  200  feet  will  require  ,rr7rr=28-f- coils. 

To  be  safe,  let  us  provide  for  00  coils,  for  which  a  length  of  drum 
(MX  :J')  +  : i~3|.  inches  is  required. 

The  space  for  brake  strap  may  be  assumed  at  5  inches,  and  the 
thickness  to  provide  necessary  strength  determined  later  in  the 
design.  The  frictional  surface  of  the  strap  may  be  of  basswood 
blocks,  say  1|-  inches  thick,  screwed  to  the  metal  band.  The 
diameter  of  brake  surface  may  be  2s  inches. 

Driving  Gears.  The  size  of  drum  gear  evidently  depends 
upon  the  method  of  fastening  to  the  drum,  and,  other  things  being 
equal,  should  be  kept  as  small  as  possible.  One  way  would  be  to 
key  the  gear  on  the  outside  of  the  drum,  another  to  bolt  the  gear 
to  the  end  ot  the  drum.  The  latter  has  the  advantage  that  a 
standard  gear  pattern  can  be  used  with  the  slight  change  of 


38 


MACHINE  DESIGN 


27 


addition  of  bolt  flange  on  the  arms.  This  makes  (a  simple,  direct, 
and  strong  drive,  the  bolts  being  in  shear. 

Sketching  this  arrangement  as  the  preferred  one  (Fig.  2A),  it 
is  evident  that  the  diameter  of  the  gear  should  be  at  least  as  large 
as  the  drum  in  order  to  keep  the  tooth  load  down  to  a  reasonable 
figure.  On  the  other  hand,  if  made  too  large,  it  spreads  out  the 
machine  and  destroys  its  compactness.  As  a  diameter  of  36 
inches  is  not  excessive,  let  us  assume  this,  and  see  if  a  desirable 
proportion  of  gear  tooth  can  be  found  to  carry  the  load. 

For  a  pitch  diameter  of  36  inches  there  will  be  a  theoretical 

load  of  ^)OQx27  =3,750  pounds  at  the  pitch  line.     But  the  load 


Fig.  2A. 

on  the  tooth  must  not  only  impart  a  pull  of  5,000  pounds  to  th? 
rope,  but  must -overcome  friction  between  the  gear  teeth  in  action, 
also  between  the  drum  shaft  and  its  bearings.  Assuming  the 
efficiency  between  the  rope  and  tooth  load  to  be  95  per  cent,  the 

net  load,  therefore,  which  the  tooth  must  take  is  ^-55  —  3,947,  sav 

.95 

4,000  pounds. 


39 


28  MACHINE  DESIGN 

Assuming  involute  teeth,  and  applying  the  "Lewis"  formula, 
(Part  II,  "GearsVj: 

W=s  Xp  X  f  X  y  W=4,000 

«=6ioOO 

4,000=6,000  X  p  X/  X  .116  #=.116  (number  of  teeth 

assumed  at  75) 

p  x/= ^OOQ —  =5.7  inches  j)=circular  pitch 

/=face  of  gear 

Let/=3j3  (a  reasonable  proportion  for  machine-cut  teeth). 
Then3xp2=5.7 

p  =1/^9=1-378  inches 
The  diametral  pitch  corresponding  to  this  is 


. 

1.378 

which  is  just  between  the  regular  standard  pitches,  2  and  2J,  for 
which  stock  cutters  are  made.  To  be  safe,  let  us  take  the  coarser 
pitch,  which  is  2.  The  circular  pitch  corresponding  to  this  is 

'  t     >  =  1.57,  and  making  the  face  about  three  times  the  circular 

pitch  gives 

3  X  1.57  =  4.71,  say  4 J  inches. 

The  number  of  teeth  in  the  gear  is  then  36  X  2  =•  72. 
Referring  to  the  value  assumed  for  the  tooth  factor  in  calculation 
above,  it  is  seen  that  y  was  based  on  75  as  the  number  of  teeth, 
which  is  near  enough  to  72  to  avoid  the  necessity  of  further  check- 
ing the  result. 

The  pinion  to  mesh  with  this  gear  should  be  as  small  as  possi- 
ble in  order  to  get  a  high-speed  ratio  between  pinion  shaft  and 
drum,  otherwise  an  excessive  ratio  will  be  required  in  the  pulleys, 
making  the  large  one  of  inconvenient  size.  Small  pinions  have 
the  teeth  badly  undercut  and  therefore  weak,  13  teeth  being  the 
lowest  limit  usually  considered  desirable,  for  that  reason.  Choos- 

13 
ing  that  number,  we  have  a  pitch  diameter  of  ~^-=  6-5  in.,  which 

is  probably  ample  to  take  the  shaft  and  key,  and  still  leave  suf- 
ficient stock  under  the  tooth  for  strength.  If  made  of  cast  iron, 

O 

however,  the  pinion  teeth,  on  account  of  the  low  number,  will  be 
narrower  at  the  root  than  those  of  the  gear  of  72  teeth.  Yet  it 


40 


MACHINE  DESIGN 


was  upon  the  basis  of  the  latter  that  the  pitch  was  chosen,  for  it 
will  be  remembered  that  the  value  of  y  in  the  formula  was 
taken  at  .116.  Hence  the  pinion  will  be  weaker  than  the  gear 
unless  we  make  it  of  stronger  material  than  cast  iron,  of  which 
the  large  gear  is  supposed  to  be  made.  Steel  lends  itself  very 
readily  to  this  requirement;  and  in  practice,  pinions  of  less  than  20 
teeth  are  usually  made  of  this  material,  hence  we  shall  specify  the 
pinion  to  be  of  steel. 

Pulleys.  The  question  now  is  whether  or  not  we  can  get  a 
suitable  ratio  in  the  pulleys  without  making  the  large  one  of  incon- 
venient size,  or  giving  the  motor  too  slow  speed  for  an  economical 
proportion. 

Suppose  we  limit  ourselves  to  a  diameter  of  42  inches  for  the 
large  pulley,  and  try  a  ratio  of  4  to  1  ;  this  will  give  a  diameter 
for  the  small  pulley  of  -4^=10J  inches.  "We  shall  then  have 

Total  ratio  between  drum  and  motor  ........   —X.  4=^=22.2 

Rev.  per  min.  of  drum  to  give  150  f.  p.  m.  of 


Eev.  per  min.  of  motor  ............  .  .........  22.2  X  21.2=470 

Horse-power  of  motor  at  80  per  cent  efficiency    V*V  X  5'(X^)=30 

33}(XX)  X    •80 

A  30  H.  P.  motor  running  470  r.  p.  m.  would  be  classed  as  a 
slow  speed  motor  and  would  be  a  heavier  machine  and  cost  mora 
than  one  of  higher  speed.  It  will  be  noticed,  however,  that  the 
diameter  of  the  small  pulley  is  already  quite  reduced,  and  it  is 
hardly  desirable  to  decrease  it  still  further.  Neither  can  we 
increase  the  large  pulley,  as  we  have  already  set  the  limit  at  42 
inches.  Hence,  for  our  present  problem  we  cannot  improve  mat- 
ters much  without  increasing  the  size  of  the  large  gear,  which  is 
undesirable,  or  putting  in  another  pair  of  gears,  which  is  contrary 
to  the  conditions  of  the  problem.  As  such  a  motor  is  perfectly 
reasonable,  we  shall  assume  it  to  be  chosen  for  the  purpose. 

In  commercial  practice  it  would  be  well  to  pick  out  some 
standard  make  of  motor  of  the  required  horse-power,  note  the  speed 
as  specified  by  the  makers,  and  then,  if  possible,  suit  the  ratio  in 
the  machine  to  this  speed.  It  is  always  best  to  use  standard  ma. 
chinery,  if  possible,  both  from  the  standpoint  of  first  cost,  as  well 


11 


30  MACHINE  DESIGN 


7^. 
-7;=   7^ 


^  •£  =  4-oo^6-<s. 


-] r  __  'ty/O'*  <=>•/*+•'''&   x/^-£_  /?  4^  ^. 

/  -^-    ~\    /  sj 

•-.o/S~ 


so 


r, 

T^-T0--    &^- 

T~-£r^  ££&-'**• 

•'   T    -    ^^'•5'  "    ^    5~<^ 
"""  /-^ 


£ 


42 


MACHINE  DESIGN 


31 


as  ease  of  replacing  worn  parts.  Machinery  ordered  special  is 
expensive  in  first  cost  of  designing,  patterns,  and  tools,  and  extra 
spare  parts  for  emergency  orders  are  not  often  kept  on  hand. 

Tabulation  of  Torsional  Moments.  For  future  reference,  it  is 
desirable  at  this  point  to  tabulate  the  torsional  moment,  or  torque, 
about  each  of  the  three  shaft  axes,  assuming  reasonable  efficiencies 
for  the  various  parts,  as  follows: 

Efficiency  between  drum  and  gear  tooth 95  per  cent 

Efficiency  between  drum  and  pinion  shaft 90  per  cent 

Efficiency  between  drum  and  motor  shaft 80  per  cent 

TABLE    OF  TORSIONAL  MOMENTS. 


Axis. 


Inch  Lbs.  Torque 
at  100  Per  Cent  Efficiency. 


Inch  Lbs.  Torque, 
Efficiency  as  Above. 


Drum 

Pinion 

Motor 


5,OOOX^ 


27 


'67,500 


6,000XX       ......  =12,187 


XX=  3,047 


This  means  that  the  motor  develops  a  torque  of  3,809  inch. 
pounds  delivering  to  pinion  shaft  13,541  inch-pounds,  and  to  drum 
71,052  inch-pounds. 

Width  of  Belt.  The  page  of  calculation  for  belt  width  is  repro. 
duced  in  Fig.  3. 

The  calculation  as  given  is  strictly  scientific,  based  on  the 
working  strength  of  a  cemented  joint  (#=400  Ibs.  per  square  inch). 
This  is  a  favorable  situation  for  the  use  of  a  cemented  joint,  be- 
cause it  is  easy  to  provide  means  of  adjusting  the  belt  tension  by 
placing  the  motor  on  a  sliding  base.  Otherwise  a  laced  joint  could 
be  used,  requiring  relacing  when  the  belt  slackens  through  its 
stretch  in  service.  Under  the  assumption  that  a  double  laced  belt 
is  used,  the  empirical  formula  below  is  one  often  applied: 


__          ,300 
~~540~-    "540" 

Thia  gives  w—  -y-^r-—  12-4  inches  (say  12  inches). 

It  should  be  remembered  that  this  value  is  purely  empirical; 
it  applies  to  a  laced  joint,  and  could  not  be  expected  to  check  the 


43 


32  MACHINE  DESIGN 

value  of  9  inches  obtained  by  the  first  computation  for  a  cemented 
joint.  It  is  fairly  in  proportion.  For  the  quite  definite  service 
req aired  of  the  belt  in  the  present  case,  the  width  of  9  inches  is 
doubtless  sufficient,  considering  the  cemented  joint.  , 

Length  of  Bearings.  Considerable  latitude  in  choice  of  length 
of  bearings  is  permissible,  especially  in  such  slow-speed  machinery. 
There  is  probably  little  danger  from  heating,  and  the  question  then 
becomes  one  of  wear.  It  is  better  in  such  cases  as  the  one  in  ques- 
tion, to  choose  boldly  a  length  which  seems  to  be  reasonable  and 
proceed  with  the  design  on  that  basis,  even  if  the  length  be  later 
found  out  of  proportion  to  the  shaft  diameter,  than  to  waste  too 
much  time  in  the  preliminary  calculation  over  the  exact  determina- 
tion of  this  question.  Probably  in  most  cases  of  commercial  prac- 
tice the  existence  of  patterns,  or  some  other  practical  consideration, 
will  decide  the  limits  of  length. 

In  the  present  instance  it  seems  reasonable  that  a  length  of 
6  inches  would  fill  the  requirement  for  the  worst  case,  that  of  the 
drum  shaft,  and  it  is  obvious  that  the  bearings  for  the  pinion  shaft 
would  naturally  be  of  the  same  length  on  account  of  being  cast  on 
the  same  bracket,  and  faced  at  the  same  setting  of  the  planer  tool. 

Height  of  Centers.  The  large  pulley  should  naturally  swing 
clear  of  the  floor.  This  will  require,  say,  a  total  height  of  23 
inches,  out  which  we  may  take  4  inches  for  the  base,  leavino-  19 
inches  as  the  height,  center  of  bearing  to  base  of  bracket. 

Data  on  Sketch.  The  data  as  found  above  should  now  be  put 
on  the  sketch  previously  made;  it  will  then  have  the  appearance 
shown  in  Fig.  1. 

This  sketch  is  now  in  form  to  control  all  the  subsequent  detail 
design,  and  it  is  expected  that  the  figured  dimensions  as  shown  can 
be  maintained.  It  is  impossible  to  predict  this  with  positiveness, 
however,  as  in  the  working  out  of  the  minor  details  certain 
may  be  found  desirable,  when,  of  course,  they  should  be  made/ 

The  shaft  sizes  do  not  appear  on  this  sketch,  hence  before 
proceeding  further  the  several  shaft  diameters  must  be  calculated. 

Sizes  of  Shafts.  The  calculations  of  the  shaft  diameters  are 
good  instances  of  systematic  engineering  computations,  hence  thej 
are  reproduced  in  the  exact  form  in  which  they  were  made.  The 
student  should  learn  a  valuable  lesson  in  making  and  recording 


MACHINE  DESIGN 


calculations  by  following  these  carefully.  Note  that  each  set  of 
figures  is  independent,  both  in  the  statement  of  given  data,  as  well 
as  in  the  actual  computation.  Observe  how  easy  it  would  be  for 
the  author  of  these  figures  or  anyone  else  to  check  them  even  after 


105<? 


Fig.  4. 

a  long  lapse  of  time.  If  the  machine  should  unexpectedly  fail  in 
service  the  figures  are  always  available  to  prove  or  disprove  theor- 
etical weakness.  The  right  triangles  merely  indicate  that  the 
value  of  v/BHT2  was  found  by  the  graphical  method  suggested  in 


MACHINE  DESIGN 


Part  II,  "  Shafts,"  the  figures  being  put  on  the  triangle  as  a  sim- 
ple and  direct  way  of  recording  both  process  and  result. 

Attention  is  especially  called  to  the  fact  that  in  the  pinion 
shaft  the  size  is  changed  for  each  piece  upon  the  shaft.     This  is 


<£-/  'o  3 


1051 


7565 


s.  / 


=    JZ 


done  partly  because  it  is  desired  to  show  tl  3  student  that  the  shaft 
at  each  of  these  points  should  be  theorel  ically  of  different  size. 
It  is  also  done  because  as  a  practical  feature  of  construction  it  is  a 
good  plan  to  change  the  size  when  the  fit  changes,  partly  for  rea. 
sons  of  production  in  the  shop,  partly  for  ease  in  slipping  pieces 


MACHINE  DESIGN 


35 


freely  endwise  on  the  shaft  until  they  reach  their  proper  fit  and 
location  in  the  assembling  of  the  machine. 

This  should  not  be  taken  as  an  absolute  requirement  in  any 
sense.  A  straight  shaft  would  be  satisfactory  in  the  present  case; 
but  the  shouldered  shaft  is  a  little  better  construction,  in  a  mechan- 
ical sense,  and  does  not  cost  much  more.  Hence  it  is  used.  For 
the  drum  the  straight  shaft  seems  to  answer  the  requirement  well 
enough. 


62./-03 


<*, 


Fig.  ft 

Small  Pulley  Bore.     Fig  4. 

Large  Pulley  Bore.     Fig.  5. 

Bearing  Next  to  Large  Pulley.     Fig.  6. 

The  diameter,  2J-J,  as  calculated,  is  based  on  the  supposition 
that  the  greatest  bending  moment  is  caused  by  the  belt  pull  on  the 
overhanging  pulley,  that  is,  by  the  forces  existing  at  the  left-hand 
side  of  the  center  of  the  bearing. 


47 


MACHINE  DESIGN 


But  the  pinion  tooth  load  produces  a  heaVy  bending  on  the 
shaft  in  the  bearing,  the  shaft  in  this  case  acting  as  a  beam  sup- 


t&zrrts 


Fig.  7. 


ported  at  the  two  bearings  and  living  the  tooth  load  applied  as 
shown.     If  this  latter  effect  be  greater  than  the  former,  that  is,  if 


48 


MACHINE  DESIGN  87 

the  bending  moment  produced  by  the  pinion  tooth  load  be  greater 
than  the  bending  moment  produced  by  the  belt  pull,  then  the  diam- 
eter must  be  increased  to  satisfy  the  latter  case.  As  is  seen  by 
the  second  calculation  of  Fig.  6,  this  is  not  the  case,  and  the  diam- 
eter stands  at  2|J  as  made. 

Pinion  Bore.  Fig.  7.  The  pinion  being  a  driving  fit  upon 
the  shaft,  reinforces  the  shaft  to  such  an  extent  that  it  is  hardly 
possible  for  the  shaft  to  break  off  very  far  inside  the  face  of  the 
pinion;  but  it  is  quite  possible  that  the  metal  of  the  pinion  may  • 
give  enough,  or  be  a  little  free  at  the  ends  of  the  hole,  so  that  the 
shaft  may  be  broken  off,  say  -|  inch  inside  the  face.  In  this  case, 
it  may  fail  from  the  moment  of  the  force  at  the  left-hand  bearing 
or  of  that  at  the  right.  It  may  fail  then  at  (a)  or  (b),  depending 
on  which  section  has  the  greater  bending  moment.  Trying  both, 
it  is  seen  by  the  calculation  that  the  right-hand  moment  is  the 
controlling  one,  and  it,  therefore,  is  used. 

Shaft  Outside  of  Pinion.  Fig.  8.  As  there  is  no  power 
transmitted  through  this  portion  of  the  shaft,  there  is  no  torsional 
moment  in  it,  and  the  bending  moment  remains  practically  the 
same  as  inside  the  pinion. 

The  size  figures  about  2j|,  but  since  there  is  no  use  in  turn- 
ing off  material  just  to  reduce  the  size  to  this,  it  is  well  to  make 
it  2|,  or  just  smaller  than  the  fit  in  the  pinion. 

Pinion  Shaft  Outer  Bearing.  Fig.  8.  This  diameter,  of 
course,  figures  small,  as  there  is  no  torsion  in  it,  and"  the  bending 
moment  is  not  heavy.  The  practical  question  comes  in,  however, 
whether  it  is  advisable,  to  make  the  outer  bracket  different  from 
the  inner  one  just  on  account  of  this  bearing.  The  commercial 
answer  to  this  would  probably  be  "No,"  hence  the  size  as  figured 
next  to  the  pinion  will  be  maintained  (2j-|). 

Drum  Shaft.  Fig.  9.  In  this  case,  as  previously  inferred, 
the  simplest  thing  to  do  is  to  use  a  piece  of  straight  cold-rolled 
steel,  and  make  both  bearings  alike,  the  size  being  determined 
according  to  the  worst  case  of  loading  which  can  occur  as  the 
rope  travels  from  end  to  end  of  the  uiim.  This  case  ia  evi- 
dently when  the  rope  is  at  the  end  of  its  travel  close  to  the  brake, 
for  at  that  time  both  the  load  on  the  rope  and  the  load  on  the  pinion 
tooth  which  is  driving  it  are  exerted  upward,  and  produce  the 


49 


MACHINE  DESIGN 


cn-eatest  reaction  at  the  bearing  next  to  the  gear.     The  analysis  of 
the  forces  for  this  condition  is  shown  in  Fig.  9. 

Other  conditions  of  loading  would  be  when  the  brake  is  on 
and  the  tooth  load  relieved,  but  then  the  resultant  of  the  brake 
strap  tensions  would  be  diagonally  downward  and  would  reduce 


.2.2'  '03 


2  Z  - 


rather  than  add  to  the  rope  load.  Again,  when  the  rope  is  at 
the  end  of  the  drum  farthest  from  the  gear,  the  load  on  it  and 
the  load  on  the  pinion  tooth  are  both  exerted  upward  as  before,  but 
the  reaction  cannot  be  ab  jreat  as  in  the  case  of  Fig.  9,  because  the 
tooth  load  is  still  concentrated  at  the  other  end  of  the  shaft  and 
produces  a  relatively  small  reaction  at  the  rope  end 


MACHINE  DESIGN 


39 


Preliminary  Layout.  Fig.  10.  Proceeding  now  with  the  lay- 
out to  scale,  the  detail  of  the  parts  may  be  worked  out  as  com- 
pletely as  the  scale  of  the  drawing  will  permit.  The  work  on  this 
drawing  may  be  of  an  unfinished,  sketchy  nature,  but  the  measure- 
ments must  be  exact  as  far  as  they  go,  for  this  drawing  is  to  serve 
as  the  reference  sheet,  from  which  all  future  detail  is  to  be  worked  up. 

In  this  layout  may  be  worked  out  the  sizes  of  the  arms  and 
hubs  of  pulleys  and  gears,  the  proportions  of  the  drum  and  brake 


T 

^f 

i 

OOO& 

*S.  o>v  O0«>v"T«0/K 

,50  o  o  '€oS  .  <MV  AXX|»€^ 

< 

^ 

•J 

3/4: 

t    r^ 

2 

"~\\ 

1/^1 

a  P-3 

x^ 

\ 

*  («* 

-^ 

r< 

/  > 

per 

t 

<  £,        > 

J2^"— 

^4 

i. 

~t 

««-* 

"Px  3^.75 
T  - 


"^  -f-  -4-OOO 


Fig.  9. 

strap,  and  the  general  dimensions  of  the  side  brackets  and  the 
base.  When  the  detail  becomes  too  fine  to  work  out  to  advan- 
tage on  this  drawing  it  may  be  worked  out  full  size  by  a  separate 
sketch,  or  left  to  be  finished  when  it  is  regularly  detailed.  The 
preliminary  layout,  it  should  be  remembered,  is  a  service  sheet 
only,  a  means  of  carrying  along  the  design,  and  not  intended  for 


51 


Fig.  10. 


MACHINE  DESIGN  41 

a  finished  drawing.  The  moment  that  the  free  use  of  the  layout 
is  impaired  by  trying  to  make  too  much  of  a  drawing  of  it,  ita 
value  is  largely  lost.  A  designer  must  have  some  place  to  try  out 
his  schemes  and  devices,  and  the  layout  drawing  is  the  place  to  do 
it.  This  drawing  may  be  recurred  to  at  intervals  in  the  progress 
of  the  design,  details  being  filled  in  as  they  are  worked  out,  as 
they  may  control  the  design  of  adjacent  parts. 

As  the  discussion  of  the  design  of  each  of  the  members 
involved  in  the  present  problem  can  be  better  taken  up  in  con- 
nection with  the  detail  drawing  of  each,  it  will  be  given  there, 
rather  than  in  connection  with  the  layout,  although  many  of  the 
proportions  thus  discussed  could  be  worked  out  directly  from  the 
latter. 

Pulleys.  Fig.  11.  The  analysis  of  the  forces  in  the  belt 
gives,  according  to  the  calculation  of  Fig.  3,  a  tension  in  the  tight 
side  of  1,059  pounds,  and  in  the  slack  side  414  pounds.  The 
difference  of  these,  or  1,059  —  414=645  pounds,  is  transmitted  to 
the  pulley  and  produces  the  torque  in  the  shaft.  Of  course  in 
the  small  pulley  the  torque  is  transmitted  from  the  motor  through 
the  pulley  to  the  belt,  but  both  cases  are  the  same  as  far  as  the 
loading  of  the  pulleys  is  concerned. 

The  only  other  force  theoretically  acting  is  the  centrifugal 
force  due  to  the  speed  of  the  pulley.  This  produces  tension  in 
the  rim  and  arms,  but  for  the  low  value  of  1,300  feet  per  minute 
peripheral  velocity  in  this  case  may  be  disregarded. 

Considering  the  arms  as  beams  loaded  at  the  ends,  and  that 
one-half  the  whole  number  of  arms  take  the  load,  and  for  con. 
venience,  figuring  the  size  of  the  arms  at  the  center  of  the  pulley 
gives  the  following  calculation  for  the  large  pulley: 

61§X21=^I=.0393X2,500X&8  Let     8=2,500 

«       A=rbreadthofoval 

h*=  *'5^  =46        .  -    .47i=  thickness  of  oval 

vo.ZD 

(say  3.5) 


.4fc=.4x3  5=1.4  (say  1  7-16) 

This  is  about  all  the  theoretical  figuring  nece3sary  on  thia 
pulley.  The  rim  is  made  as  thin  as  experience  judges  it  capable 
of  being  cast;  the  arms  are  tapered  to  suit  the  eye,  thus  giving 
ample  fastening  to  the  rim  to  provide  against  shearing  off  the  rim 


5:5 


MACHINE  DESIGN  43 

from  the  arms;  generous  fillets  join  the  arms  to  both  rim  and  hub; 
and  the  hub  is  given  thickness  to  carry  the  key,  and  length 
enough  to  prevent  tendency  to  rock  on  the  shaft.  Uncertain 
strains  due  to  unequal  cooling  in  the  foundry  mold  may  be  set  up 
in  the  arms  and  rim,  but  with  careful  pouring  of  the  metal  they 
should  not  be  serious,  and  the  low  value  chosen  for  the  fibre  stress 
allows  considerable,  margin  for  strength. 

The  small  pulley  has  the  same  forces  to  withstand  as  the 
large  pulley,  but  on  account  of  its  small  diameter  there  is  not 
room  enough  for  arms  between  the  rim  and  the  hub,  hence  it  is 
made  with  a  web.  The  web  cannot  be  given  any  bending  by  the 
belt  pull,  the  only  tendency  which  exists  in  this  case  being  a 
shearing  where  the  web  joins  the  hub.  This  shearing  also  exists 
throughout  the  web  as  well,  but  at  other  points  farther  from  the 
center  it  is  of  less  magnitude,  and  moreover,  there  is  more  area  of 
metal  to  take  it.  The  natural  way  to  proportion  the  thickness  of 
the  web  is  to  give  it  an  intermediate  thickness  between  that  of  the 
hub  and  rim,  thus  securing  uniform  cooling,  and  then  figure  the 
stress  as  a  check.  Making  this  value  ^  inch  gives  a  shearing  area 
of  g-  multiplied  by  the  circumference  of  the  hub,  which  is  3.1416 


X  4  =  12.56.     The  shearing  force  at  the  hub  is  -—  =1,693 

pounds.     Equating  the  external  force  to  the  internal  resistance 
1,693  =^JX  12.56X8 

S  ~  jy  10  5C  =  "^  Poun(*s  Per  S(luare  incn  (approx.). 

This  is  a  very  low  figure,  even  for  cast  iron,  hence  the  web  is 
amply  strong.  The  rim  and  hub  are  proportioned  as  for  the  large 
pulley. 

The  keys  are  taken  from  the  standard  list.  They  may  be 
checked  for  shear,  crushing  in  the  hub,  and  crushing  in  the  shaft, 
but  the  hubs  are  so  long  that  it  is  at  once  evident  without  figuring 
that  the  stress  would  run  very  low  in  both  cases. 

Gears.  Fig.  12.  The  analysis  of  the  forces  acting  on  the 
gears  has  been  given  on  page  28,  4,000  pounds  being  taken  at  the 
pitch  line.  Using  this  same  value,  and  choosing  a  T-shaped 
arm  as  a  good  form  for  a  heavily  loaded  gear  like  the  present  one, 
let  us  consider  that  the  rim  is  stiff  enough  to  distribute  the  load 


J 


v£ 


Fig.  12. 


MACHINE  DESIGN  45 

equally  between  all  the  arms,  and  that  each  acts  as  a  beam  loaded 
at  the  end  with  its  proportion  of  the  tooth  load.  Before  we  can 
determine  the  length  of  these  arms,  however,  we  must  fix  upon  the 
size  of  the  flange  which  is  to  carry  the  driving  bolts.  This  is  taken 
at  13  inches.  It  could  be  smaller  if  desired,  but  drawing  the  bolts 
in  toward  the  center  increases  the  load  on  them,  and  13  inches 
seems  reasonable  until  it  is  proved  otherwise.  This  makes  the 

maximum  moment  which  can  come  on  an  arm  —  — = 7,666 

6 

inch-pounds. 

Now  it  is  evident  that  the  base  of  the  T  arm  section,  which 
lies  in  the  plane  of  rotation,  is  most  effective  for  driving,  and 
that  the  center  leg  of  the  T  does  not  add  much  to  the  driving 
capacity  of  the  arm,  although  it  increases  the  lateral  stiffness  of 
the  arm,  as  well  as  providing  in  casting  a  free  flow  of  metal  between 
the  rim  and  the  hub.  Hence  the  simplest  way  of  treating  the  sec- 
tion of  the  arm  for  strength  is  to  consider  the  base  of  the  T 
only,  of  rectangular  section,  breadth  J,  and  depth  /*,  for  which 

.    SX^XA2. 

the  internal  moment  of  resistance  is  ~ 

o 

Also,  it  is  simplest  to  assume  one  dimension,  say  the  breadth, 
and  the  allowable  fibre  stress,  and  figure  for  the  depth.  Taking 
the  breadth  at  1J  inches,  which  looks  about  right,  and  the  fibre 
stress  at  2,500,  and  equating  the  external  moment  to  the  internal, 
we  have 

3,500X1.125X7,* 

6X7,666 

~- 2,500X1.125" 
h  =.j/IO  =  4.05  (say  4J) 

Drawing  in  this  size,  and  tapering  the  arm  to  the  rim  as  in 
the  case  of  the  pulleys,  making -the  depth  of  the  rim  according  to 
the  suggested  proportions  given  in  Part  II,  "  Gears,"  giving  the 
center  leg  of  the  T  a  thickness  of  ^  inch  tapering  to  1  inch,  and 
heavily  filleting  the  arms  to  the  rim  and  center  flange,  we  have  a 
fairly  well  proportioned  gear. 

The  next  thing  to  determine  is  the  size  of  the  driving  bolts. 
The  circle  upon  which  their  centers  lie  may  be  11  inches  in  diam- 


57 


Fig.  13. 


MACHINE  DESIGN  47 

eter,  and  there  will  naturally  be  six  bolts,  one  between  each  arm. 
These  bolts  are  in  pure  shear,  and  the  material  of  which  thoy  are 
to  be  made  ought  to  b3  good  for  at  least  8,000  pounds  per  square 
inch  fibre  stress.  The  force  acting  at  the  circumference  of  an 

11-inch  circle  would  be  — — =-= — -==13,091  pounds. 

Equating  the  load  on  each  bolt  to  the  resisting  shear  gives 

13.091    £  .      8,OOOX3.U16X<22      Let  A = area  resisting  shear. 

-"j£-=8tOOOX  A=-       — —  Let  rf=dia>  of  bolt 

Then  A=^ 

4X13,091 

"~6X8,OOOX3.1416~" 
d=  1/135"  (say  ,6)     %-mch  bolts  would  do. 

But  f -inch  bolts  are  pretty  small  to  use  in  connection  with  such 
heavy  machinery.  They  look  out  of  proportion  to  the  adjacent 
parts.  Hence  -|-ineh  bolts  have  been  substituted  as  being  better 
suited  to  the  place  in  spite  of  the  fact  that  theoretically  they  are 
larger  than  necessary.  The  extra  cost  is  a  small  matter.  These 
bolts  may  crush  in  the  flange  as  well  as  shear  off,  but  as  there  is 

13  091 
an  area  of  |xlf  =  1.422  square  inches  to  take — ^ —  =2,182 

pounds,  the  pressure  per  square  inch  of  projected  area  is  only 

2,182 

.'     9=1,534  pounds,  which  is  very  low. 

This  gear  needs  no  key  to  the  shaft  because  all  the  power 
comes  down  the  arms  and  passes  off  to  the  drum  through  the  bolts, 
thus  putting  no  torsional  stress  in  the  shaft.  The  face  of  the 
flange  is  counterbored  so  as  to  center  the  gear  upon  the  drum, 
without  relying  upon  the  fit  of  the  gear  upon  the  shaft  to  do  this. 

The  pinion  is  solid  and  needs  no  discussion  for  its  design. 

Brackets  and  Caps.  Fig.  13.  As  the  size  of  the  drum  shaft 
was  determined  by  considering  the  rope  wound  close  up  to  the 
brake,  thus  giving  in  combination  with  the  load  on  the  gear  tooth 
the  maximum  reaction  at  the  bearing  as  6,748  pounds,  the  cap  and 
bolts  should  be  designed  to  carry  the  same  load. 

For  a  bearing  but  6  inches  long,  two  bolts  are  sufficient  under 
ordinary  conditions  and  might  perhaps  do  for  this  case. .  The  load 
is  pretty  heavy,  however,  and  it  is  deemed  wise  to  provide  four 
bolts,  thus  securing  extra  rigidity,  and  permitting  the  use  of  bolts 


59 


43  MACHINE  DESIGN 

of  comparatively  small  si/e.  If  the  load  were  distributed  equally 
over  all  the  bolts  each  would  take  one-fourth  of  the  whole  load, 
but  it  is  not  usually  safe  to  figure  them  on  this  basis,  because  it 
is  difficult  to  guarantee  that  each  bolt  will  receive  its  exact  share 
of  stress.  Assuming  that  the  two  bolts  on  one  side  take  J  the 
whole  load  instead  of  .',,  which  provides  for  this  uncertain  extra 
stress,  each  bolt  must  take  care  of  -*-  of  0,74-S,  or  2.240,  pounds. 
Allowing  8,000  pounds  per  square  inch  fibre  stress  calls  for  an 

2,24(.) 
area  at  the  root  of  the  thread  of  ,      ,  T  —  .281    square   inch.     Con- 

sulting a  table  of  bolts  we  find  that  the  next  -standard  size  of  bolt 
greater  than  this  is  -^,  which  gives  an  area  of  .302-  square  inch. 

Choosing  this  size  as  satisfactory,  the  bolts  should  be  located 
as  close  to  the  shaft  as  will  permit  the  hole  to  be  drilled  and  tapped 
wituout  breaking  out.  A  center  distance  of  5.1,  inches  accomplishes 
this  result.  The  distance  between  centers  in  the  other  direction 
is  somewhat  arbitrary,  although  the  theoretical  distance  between 
the  bolt  and  the  end  of  the  bearing  to  give  equal  bending  moment 
at  the  center  of  the  cap  and  at  the  line  of  the  bolts  is  about  -/f  of 
the  length,  or  -254-  of  (>--!_]-  inches.  This  proportion  answers 
well  for  the  present  case,  although  for  long  caps  it  brings  the 
bolts  too  far  in  to  look  well. 

The  thickness  of  the  cap  may  be  determined  by  assuming  it 
to  be  a  beam  supported  at  the  bolts  and  loaded  at  the  middle. 
This  is  not  strictly  true,  for  the  load  is  distributed  over  at  least  a 
portion  of  the  shaft  diameter;  moreover,  the  bolts  to  some  extent 
make  the  beam  fixed  at  the  ends.  It  Ix-ing  impossible  to  determine 
the  exact  nature  of  the  loading,  we  may  take  it  as  stated,  supported 
at  the  ends  and  loaded  in  the  middle,  and  allow  a  higher  fibre 
stress  than  usual,  say  8,500.  The  longitudinal  section  at  the 
middle  of  the  cap  is  rectangular,  of  breadth  i\  inches,  and  der>th 
unknown,  say  //.  The  equation  of  moments  is 

^Y    ZSI      S.l>,' 


-  <  6 

(y  48  X  5.5       3,500  x  fi  x  7,2 


4X3,500X0- 
h  =  1/2JB5=1.G2  (1  j  will  probably  answer) 


60 


MACHINE  DESIGN  49 

For  the  other  bearing  next  to  the  pinion,  the  load  on  the  tooth 
acts  downward,  and  the  resultant  pull  of  the  belt  is  nearly  hori- 
zontal, hence  the  cap  and  bolts  must  stand  but  little  load,  and 
calculation  would  give  minute  values.  In  a  case  like  this  it  is 
well  to  make  the  size  the  same  as  for  the  larger  bearing,  unless 
the  contraction  becomes  very  clumsy  thereby.  This  saves  chang- 
ing drills  and  taps  in  making  the  holes,  and  preserves  the  symmetry 
of  the  bracket.  The  |-inch  bolts  are  good  proportion  for  the 
smaller  bearing,  hence  that  size  will  be  maintained  throughout. 

The  body  of  the  bracket  is  conveniently  made  with  the  web  at 
the  side  and  horizontal  ribs  extending  to  the  outside.  The  lotid  due 
to  the  rope  is  carried  directly  down  the  side  ribs  and  web  into 
the  bottom  flanges  and  to  the  bolts.  The  analysis  of  the  forces 
on  these  bolts  is  shown  in  Fig.  14.  It  is  evident  from  the  figure 
that  the  resultant  belt  pull  tends  to  hold  the  bracket  down,  while 
the  load  on  the  rope  tends  to  pull  it  -up,  the  point  about  which  it 
tends  to  rotate  being  the  corner  furthest  from  the  drum.  It  is  also 
evident  thac  the  bolts  nearest  this  corner  can  have  little  effect  on 
the  holding  down,  because  their  leverage  is  so  small  about  the  cor- 
ner,  hence  we  shall  assume  that  the  pair  of  bolts  at  the  right-hand 
end  of  the  bracket  takes  all  the  load.  The  belt  pull,  being  hori- 
zontal. tends  to  slide  the  bracket  along  the  base,  but  this  tendency 
is  email,  and  at  any  rate  is  easily  taken  care  of  by  the  two  dowel 
pins,  which  are  thus  put  in  shear. 

The  load  on  the  bolts  being  4,954  pounds,  a  heavy  bending 
moment  is  thrown  on  the  flange  of  the  bracket,  tending  to  break 
it  off  at  the  root  of  the  fillet.  The  distance  to  the  root  of  the  fillet 
is  2  inch;  the  section  tending  to  break  is  rectangular,  of  breadth 
51,  inches,  and  unknown  depth  //.  The  equation  of  moments  ia 


6 
6x4,954x3 


=  1.3  (  say  1J). 

The  thickness  of  the  web  and  ribs  of  this  bracket  is  hardly 
capable  of  calculation.     The  figure  |  inch  has  been  chosen  in  pro- 


Gl 


50 


MACIIIXE  DESIGN 


portion  to  tlio  size  of  the  largo  drum  bearing,  givino-  ample  stiff- 
ness and  rigidity,  and  permitting  uniform  flow  and  cooling  of  the 
metal  in  the  mold.  The  opening  in  the  center  is  made  merely  to 
save  material,  as  in  that  part  little  stress  would  exist,  the  two  sides 


5000 


Sgj 

/   ^  •Inh, 

—  I 

—       T   ~  I  r>  ^ft 

<                   3~  ''  " 

W  = 


;w 

+  IfT'ixl 

—  m-7  2>  x 


2>  7,  &  7 


O    /  y  *y   -y 


WUJjJl 


ft 


Carrying  tlio  load  down  to  the  base  bolts,  and  the  top  serving  as  a 
tie  between  the  bearings. 

This  bracket  might  be  made  with  the  \veb  in  the  center  of  the 
tarings  instead  of  at  the  side,  in  which  case  the  expense  of  the 


MACHINE  DESIGN  51 

pattern  would  be  slightly  greater.  It  could  also  be  made  of  closed 
box  form,  but  would  in  that  case  probably  weigh  more  than  as 
shown. 

Drum  and  Brake.  Fig.  15.  The  analysis  of  the  forces  acting 
on  the  drum  is  simple,  but  its  theoretical  design  is  more  compli- 
cated. It  is  evident  that  the  drum  acts  as  a  beam  of  hollow  circular 
cross  section,  and  that  its  worst  case  of  loading  is  when  the  rope  is 
at  or  near  the  middle  of  the  drum  length.  At  the  same  time  the 
metal  of  this  circular  cross  section  is  in  a  state  of  torsion  between 
the  free  end  of  the  rope  and  the  driving  gear,  due  to  the  load  on 
the  gear  tooth  and  the  reaction  of  the  rope.  Also  the  wrapping  of 
the  rope  around  the  drum  tends  to  crush  the  metal  of  the 
section  beneath  it,  the  maximum  effect  of  this  action  being  near 
the  free  end  of  the  rope  where  its  tension  has  not  been  reduced  by 
friction  on  the  drum  surface. 

Now  the  "  mechanics "  to  solve  the  problem  of  these  three 
combined  actions  is  rather  complicated.  It  can  JDO  at  least  approx- 
imately solved,  however,  for  it  _  satisfies  fairly  well  the  case  of 
combined  compression  and  shear.  But  on  a  further  study  of  this 
particular  case,  it  is  seen  at  once  that  the  diameter  of  the  drum  is 
relatively  large  with  respect  to  its  length,  which  means  that  the 
thickness  of  the  metal  may  be  very  small  and  yet  give  a  large 
resisting  area,  or  value  of  "I,"  both  in  direct  bonding  as  well  as 
torsion;  also  it  is  so- short  that  the  external  bending  moment  will 
be  small.  The  practical  condition  now  comes  in,  that  the  drum 
can  be  safely  cast  only  when  the  thickness  of  the  metal  is  at  a 
minimum  limit,  for  the  core  may  be  out  of  round,  not  set  centrally, 
or  by  some  other  variation  produce  thin  spots  or  even  develop  holes 
reaching  out  into  the  rope  groove,  discovered  only  when  the  latter 
is  turned  in  the  lathe. 

Hence  it  seems  reasonable  and  safe  in  this  case  to  make  the 
thickness  of  the  drum  depend  simply  upon  the  crushing  caused  by 
the  wrapping  of  "the  rope  around  it,  and  we  shall  take  the  coil 
nearest  the  free  end  of  the  rope,  assuming  that  it  carries  the  full 
load  of  5,000  pounds  throughout  one  complete  wrap  around  the 
drum. 

The  area  resisting  the  crushing  action  may  be  considered  to 
be  that  of  the  cross  section  of  a  ring,  of  width  equal  to  the  pitch 


63 


Fig.  15, 


MACHINE  DESIGN  53 


of  the  groove.  Assuming  that  |  inch  is  the  least  thickness  which 
can  be  safely  allowed  under  the  groove  for  casting  purposes,  let 
us  figure  the  crushing  fibre  stress  to  see  if  this  is  sufficiently 
strong.  Disregarding  the  small  amount  of  metal  existing  above 
the  bottom  of  the  groove,  this  gives  the  area  to  resist  the  crushing 
|X|=  ?r|,  or  .47  inch.  Since  there  are  two  of  these  sections  ana 
the  rope  acts  on  both  sides,  the  equation  of  forces  is: 
5,000X2  =  Sx.47x2 

5  00()  X  2 
S  =    \^ — ~    =  10620  pounds  per  square  inch. 

"This,  for  cast  iron,  in  pure  crushing,  allows  plenty  of  margin 
for  the  extra  bending  and  torsional  stress,  which  for  such  a  con- 
siderable thickness  would  bs  slight. 

The  above  case  indicates  a  method  of  reasoning  much  used  in 
designing  machinery,  which  while  following  out  the  specified 
routine  of  thought  as  previously  given  in  these  pages,  stops  short 
of  elaborate  and  minute  theoretical  calculation  when  such  is  obvi- 
ously unnecessary.  If  a  drum  of  great  length  were  to  be  designed, 
and  of  small  diameter,  the  same  method  of  reasoning  would  deduce 
the  fact  that  the  design  should  be  based  on  the  bending  and  the 
torsional  moments,  the  thickness  in  such  a  case  b^ing  so  great  to 
withstand  these  that  the  intensity  of  the  crushing  due  to  wrap  of 
the  rope  becomes  of  inappreciable  value. 

The  remaining  points  of  design  of  the  drum  are  determined 
from  practical  considerations  and  judgment  of  appearance.  The 
ribs  behind  the  arms  are  put  in  to  give  lateral  stiffness  and  guard 
against  endwise  collapse.  The  arms  are  subject  to  the  same  bend- 
ing as  those  of  the  gear,  but  as  they  are  equally  heavy  it  is  not 
necessary  to  calculate  them.  The  flange  at  the  driving  end  is  of 
course  matched  to  that  already  designed  for  the  gear.  The  rope 
is  intended  to  be  brought  through  the  right-hand  end  with  an 
easy  bend  and  the  standard  form  of  button  wedged  on  to  prevent 
its  pulling  through. 

This  drum  would  probably  be  cast  with  its  axis  vertical,  and 
the  driving  flange  down  to  secure  sound  metal  at  that  point. 
Heavy  risers  would  be  left  at  the  other  end  to  secure  soundness 
where  the  rope  is  fastened.  Drums  are  often  cast  with  the  axis 
horizontal,  but  the  vertical  method  is  more  certain  to  produce 
a  sound  casting.  The  grooves  should  be  turned  from  th^ 


65 


54  MACHINE  DESIGN 

solid  metal,  partly  because  it  is  a  difficult  matter  to  cast  them,  but 
principally  because  the  rope  should  run  on  as  smooth  surface  as 
possible  to  avoid  undue  wear.  On  drums  which  carry  chain  instead 
of  \vire  rope  the  grooves  are  sometimes  cast  with  success,  although 
even  in  this  case  the  turned  groove  is  generally  preferable. 

The  brake  consists  of  a  wrought-  iron  band  to  which  are  fast- 
ened wooden  blocks,  the  iron  band  giving  the  requisite  strength 
while  the  blocks  give  frictional  grip  on  the  drum  surface  and  can 
be  easily  replaced  when  worn.  As  in  the  designing  of  a  belt  the 
object  in  view  is  the  grip  on  the  pulley  surface  by  the  leather  to 
enable  power  to  be  transmitted  from  the  belt  to  the  pulley,  so  in 
the  case  of  the  brake  if  we  put  the  proper  tension  in  the  strap  it 
can  be  made  to  grip  the  brake  drum  so  tightly  that  motion  between 
it  and  the  drum  cannot  occur.  The  latter  case  is  really  the  reverse 
of  the  first,  if  the  driven  pulley  be  considered,  but  is  identical  with 
the  case  of  the  driving  pulley,  in  which  the  power  is  transmitted 
from  the  pulley  to  the  belt.  Of  course  in  the  case  of  the  brake 
uo  power  is  transmitted,  as  when  the  brake  holds  no  motion  occurs, 
but  the  principle  of  the  relative  tensions  in  the  strap  is  the  same 
as  for  the  belt. 

Since  the  brake  drum  surface  is  28  inches  in  diameter,  the  load 
at  that  surface  which  the-  brake  must  hold  is 


P  =  =  4,821  pounds. 

JUT:  /\  ~- 

We  have  then  the  following  calculation  corresponding  exactly 
to  that  of  the  belt  given  in  Fig.  )>. 


Tn—T0=P  =  4,821 

log.  ^  =  2.720  X  .25  X  .75  =  0.512  (for  which  ^^^  DUmbef 

T  T 

Then  ±2- =3.25      T0=^;'= 
i0  ..,.,0 

Tn-T0  =  4,S21  TD-i  =  ^^5  =  4.821 


4  8°1  y  3  ^5 

Tn  =  ""2  *  '"  -  =  6,963  pounds  (say  7,000) 

T0  =  6,963—4,821  =  2.142  pounds  (say  2,200) 


MACHINE  DESIGN  55 

The  tight  end  of  the  strap  must  then  be  capable  of  carrying  a 
load  of  7,000  pounds,  and  since  the  width  has  already  been  taken  at 
4i  inches,  the  problem  is  to  find  the  necessary  thickness.    Equating 
the  external  load  to  the  internal  resistance  we  have 
7,000  —  A  X  S  Let  t  =  thickness 

"  S  =  fibre  stress  =  12,000 
7,000  =  4.5X^X12,000 


_ 

This,  however,  can  be  but  a  preliminary  figure,  for  the  riveting 
of  the  strap  will  take  out  some  of  the  effective  area,  and  the  thick- 
ness will  have  to  be  increased  to  allow  for  this.  Suppose  on  the 
basis  of  this  figure  we  assume  the  thickness  at  a  slightly  increased 
value,  say  ^  inch,  and  proceed  to  calculate  the  rivets. 

A  group  of  five  rivets  will  work  in  well  for  this  case,  which 

gives  —  '-=  —  •  =  1,400  pounds  per  rivet.     A  safe  shearing  fibre  stress 

1  400 
is  6,000,  hence  the  area  necessary  per  rivet  is  /»*QQQ  =  -23  square 

inch.  This  comes  nearest  to  the  area  T95  diameter,  but  for  the 
sake  of  using  the  more  general  size  of  rivet  (|  inch)  the  latter  is 
chosen,  for  which  the  area  is  .30. 

We  must  DOW  try  these  rivets  in  a  -^-inch  plate  for  their  safe 
bearing  value.  The  projected  area  of  a  |-inch  hole  in  a  -^ff-inch  plate 

is  |  X-&  =.117  square  inch.  -^-  =  11,965  (15,000  would  be  safe) 
Taking  out  two  ft-inch  rivets  from  the  full  width  of  4i  inches 

O  o  & 

leaves  4J  —  (2  X  g)—  3.25,  and  makes  the  net  area  of  strap  to  take 
stress  8.25  Xi\=.61  square  inches.    Re-calculating  the  fibre  stress 
for  this  area  gives 
7,000  =  .  61  XS 

~  _  7,000  =  11,475  (which  approximates  the  previous  value 

=  ~M~  of  12,000). 

The  slack  end  of  the  strap  has  to  take  but  2,200  pounds,  hence 
a  different  calculation  might  be  made  for  this  end  giving  smaller 
rivets;  but  as  it  is  impractical  to  change  the  thickness  of  the  strap 
to  meet  this  reduced  load,  it  is  well  to  maintain  the  same  propor- 
tion  of  joint  as  at  the  tight  end.  The  spacing  of  the  rivets  in  both 


67 


11 

75.- 

n 


*  * 


Fig.  16. 


MACHINE  DESIGN  §  5? 

cases  follows  the  ordinary  rule  allowing  at  least  three  times  the 
diameter  of  the  rivet  as  center  distance,  and  one-half  this  value  to 
the  edge  of  the  plate. 

c5  J 

The  threaded  end  of  the  forging  on  the  strap  also  has  to  carry 
the  load  of  2,200  pounds,  for  which  a  size  smaller  than  1  inch 
would  suffice.  It  is  natural,  however,  for  the  sake  of  general  pro- 
portion to  make  the  bolt  as  strong  as  the  strap,  and  a  1-inch  bolt 
gives  an  area  of  .52  square  inch,  nearly  equalling  the  value  of 
.61  net  area  of  strap  noted  above. 

Base,  Brake=Strap  Bracket  and  Foot  Lever.  Fig  16.  The 
base  cannot  be  definitely  calculated,  and  can  best  be  proportioned 
by  judgment.  It  must  not  distort,  twist,  or  spring  in  any  way  to 
throw  the  shafts  out  of  line.  The  area  in  contact  with  the  founda- 
tion upon  which  it  rests  must  be  ample  to  carry  the  weight  of  the 
whole  machine  with  a  low  unit  pressure.  Although  the  form 
shown  is  perfectly  practicable  to  cast  and  machine,  and  is  simple 
ard  rigid,  yet  it  is  questionable  if  a  bolted-up  construction,  say  of 
four  pieces,  might  not  be  equally  rigid  and  yet  involve  greater 
facility  of  production  in  both  the  foundry  and  machine  shop  on 
account  of  the  reduced  sizes  of  parts  to  be  handled.  This  is  a 
question  which  depends  on  the  equipment  and  methods  of  the 
individual  shop,  and  is  an  illustration  of  the  practical  control  of 
design  by  manufacturing  conditions. 

The  brake-strap  bracket  and  foot  lever,  also  shown  in  this 
figure,  are  examples  of  machine  parts  which  are  quite  definitely 
loaded,  and  the  designing  of  which  is  a  simple  matter.  Further 
discussion  of  their  design  is  not  made,  the  student  being  given 
opportunity  for  some  original  thought  in  determining  the  forces 
and  moments  that  control  their  design. 

Gear  Guard  and  Brake=Relief  Spring.  In  exposed  machin- 
ery of  this  character  it  is  desirable  to  cover  over  the  gears  with  a 
guard  to  prevent  anything  accidentally  dropping  between  the 
teeth  and  perhaps  wrecking  the  whole  machine.  This  guard  is  not 
shown,  as  it  involves  little  of  an  engineering  nature  to  interest 
the  student.  It  could  readily  be  made  of  sheet  metal  or  light 
boiler  plate,  bent  to  follow  the  contour  of  the  gears  and  fastened 
to  the  top  flange  of  the  main  bracket. 

If  the  brake  be  not  automatically  supported  at  its  top  it  will 


69 


MACHINE  DESIGN 


lie  with  considerable  pressure,  due  to  its  own  weight,  on  the  brake 
surface  when  it  is  supposed  to  be  free  fron,  :'t,  and  by  the  friction 
thereby  created  will  produce  a  heavy  drag  and  waste  of  power. 
A  spring  connection  fastened  to  an  overhead  beam  is  a  simple  way 
of  accomplishing  the  desired  result.  A  flat  supporting  strap  car- 
ried out  from  the  gear  guard,  having  some  degree  of  spring  in  it, 
is  a  neater  method  of  solving  the  problem.  The  spring  should 
be  just  strong  enough  to  counterbalance  the  weight  of  the  strap 
and  yet  not  resist  to  an  appreciable  degree  the  force  applied  to 
throw  the  brake  on. 


GENERAL  DRAWING. 

The  last  step  in  the  process  of  design  of  a  machine  is  the 
making  of  the  assembled  or  general  drawing.  This  should  be 
built  up  piece  by  piece  from  the  detail  drawings,  thereby  serving 
as  a  last  check  on  the  parts  going  together.  This  drawing  may 
be  a  cross  section  or  an  outside  view.  In  any  case  it  is  not  wise 
to  try  to  show  too  much  of  the  inside  construction  by  dotted  lines. 
for  if  this  be  attempted,  the  drawing  soon  loses  its  character  of 
clearness,  and  becomes  practically  useless.  A  general  drawing 
should  clearly  hint  at,  but  not  specify,  detailed  design.  It  is 
just  as  valuable  a  part  of  the  design  as  the  detail  drawing,  but 
it  cannot  be  made  to  answer  for  both  with  any  degree  of  success. 
A  good  general  drawing  has  plenty  of  views,  and  an  abundance  of 
Cross  sections,  but  few  dotted  lines. 

The  general  drawing  of  the  machine  under  consideration  is 
left  for  the  student  to  work  up  from  the  complete  details  shown. 
It  would  look  something  like  the  preliminary  layout  of  Fig.  10,  if 
the  same  were  carefully  carried  out  to  finished  form.  A  plain  out- 
side  view  would  probably  be  more  satisfactory  in  this  case  than  a 
cross  section,  as  the  latter  would  show  little  more  of  value  than  the 
former.  The  functions  which  the  general  drawing  may  serve  are 
many  and  varied.  Its  principal  usefulness  is,  perhaps,  in  showing 
to  the  workman  how  the  various  parts  go  together,  enabling  him  to 
sort  out  readily  the  finished  detail  parts  and  assemble  them,  finally 
producing  the  complete  structure.  Otherwise  the  making  of  a 
machine,  even  with  the  parts  all  at  hand,  would  be  like  the  putting 
together  of  the  many  parts  of  an  intricate  puzzle,  and  much  time 


i  o 


MACHINE  DESIGN  59 

would  be  wasted  in  trying  to  make  the  several  parts  fit,  with  per- 
haps never  complete  success  in  giving  each  its  absolutely  correct 
location. 

The  general  drawing  also  gives  valuable  information  as  to  the 
total  space  occupied  by  the  completed  machine,  enabling  its  loca- 
tion in  a  crowded  manufacturing  plant  to  be  planned  for,  its  con- 
nection to  the  main  driving  element  arranged,  and  its  convenience 
of  operation  studied. 

In  some  classes  of  work  it  is  a  convenient  practice  to  letter 
each  part  on  the  general  drawing,  and  to  note  the  same  letters  on 
the  specification  or  order  sheet,  thus  enabling  the  whole  machine 
to  be  ordered  from,  the  general  drawings.  This  is  a  very  excel- 
lent service  performed  by  the  general  drawing  in  certain  lines  of 
work,  but  for  such  a  purpose  the  drawing  is  quite  inapplicable 
in  others. 

Merely  as  a  basis  for  judgment  of  design,  the  general  drawing 
fulfils  an  important  function  in  any  class  of  work,  for  it  approaches 
the  nearest  possible  to  the  actual  appearance  that  the  machine  will 
have  when  finished.  A  good  general  drawing  is,  for  critical  pur- 
poses, of  as  much  value  to  the  expert  eye  of  the  mechanical 
engineer  as  the  elaborate  and  colored  sketch  of  the  architect  is  to 
the  house  builder  or  landscape  designer. 

1  O 

From  the  above  it  is  readily  understood  that  the  general 
drawing,  although  a  mere  putting  together  of  parts  in  illustration, 
is  yet  of  great  assistance  in  producing  finished  and  exact  machine 
design. 

GENERAL  COMMENTS  ON  PRECEDING  PROBLEM. 

After  following  through  the  detail  of  work  as  given  in  the 
preceding  pages,  it  is  worth  while  to  stop  for  a  moment  and 
take  a  brief  survey  or  review  of  the  subject  as  illustrated  therein. 

If  the  text  be  carefully  studied  it  will  be  seen  that  in  every 
part  to  be  designed  the  same  routine  method  has  been  followed, 
regardless  of  the  final  outcome.  In  some  cases  it  may  seem  a 
roundabout  procedure  to  follow  a  train  of  thought  that  finally 
ends  in  a  design  apparently  based  on  purely  practical  judgment, 
the  theory  having  had  but  very  little  if  any  influence.  The  ques- 
tion at  once  arises — Why  not  use  the  empirical  rule  or  formula  in 


71 


60  MACHINE  DESIGN 


the  first  place  ?  Why  not  make  a  good  guess  at  once  ?  Why  not 
save  all  the  time  and  energy  devoted  to  a  careful  analysis  and 
theory,  if  we  are  finally  to  throw  them  away  and  not  base  our 
design  on  them  '( 

The  principle  to  be  noted  in  this  connection  is.  that  it  is  just 
as  fatal  to  good  design  to  rely  upon  bare  experience  and  upon 
judgment  alone,  as  it  is  to  construct  solely  according  to  what  pure 
theory  tells  us.  There  are  many  things  in  the  operation  of 
machinery  that  are  totally  inexplicable  from  the  purely  practical 
point  of  view,  and  will  forever  remain  so  until  we  analyze  them 
and  theorize  on  them.  Many  good  things  in  machinery  have 
been  the  result  of  what  might  be  called  "reversed-'  machine 
design.  When  a  new  machine  is  started,  it  frequently,  or  we 
might  almost  say  always,  fails  to  do  its  work  just  as  it  is  expected 
to  do  it.  This  is  because  some  little  point  of  design  is  bad.  owing 
to  the  inability  of  drawings,  however  good  they  may  be.  to  show 
all  that  the  machine  itself  in  bodily  form  and  in  motion  shows. 

Now.  if  our  analysis  and  theory  have  been  good  in  the 
designing  process,  it  is  almost  sure  that  we  can  very  readily 
analyze  and  theorize  on  the  trouble  that  exists  when  the  machine 
is  finished,  can  detect  the  weakness,  and  can  correct  it  with  coin- 
paratively  small  change  in  the  general  design.  This  is  ••  reversed'' 
machine  design. 

Jf.  on  the  contrary,  we  have  based  our  design  purely  on  guess- 
work, allowing  our  fancy  full  and  free  plav  to  work  out  the  details 
without  further  basis,  we  may  consider  ourselves  lucky  if  the 
machine  runs  at  all.  This,  however,  is  not  the  worst  of  the 
situation.  If  the  machine  does  actually  operate,  even  as  well  as 
it  might  reasonably  be  expected  to.  but  still  has  the  usual  diffi- 
culty of  some  little  kink  or  hitch  that  was  not  expected,  then,  as  a 
result  of  the  method  upon  which  the  whole  thing  has  been  con- 
structed, we  have  no  definite  plan  of  action  to  proceed  upon.  We 
must  try  first  this,  then  that  scheme  to  obviate  the  trouble.  We 
may  be  fortunate  enough  to  "  strike  it "'  the  first  time  ;  we  may 
never  strike  it.  It  is  doubtful  if  the  machine  ever  can  be  made  to 
work  at  highest  efficiency  ;  and  if  fairly  good  residts  be  finally 
obtained  we  never  know  the  reason  why.  and  have  nothino-  on 
'  which  to  base  any  future  action  or  design. 


72 


MACHINE  DESIGN  61 

This  haphazard  process  is  not  machine  design  at  all,  either 
in  name  or  in  result. 

As  has  previously  been  stated  in  these  pages,  there  is  no 
such  thing  as  too  much  analysis  or  theory  in  the  designing  of 
machinery.  Even  if  we  carefully  analyze,  theorize  with  rigorous 
exactness,  and  then  practically  modify  our  construction  to  such  a 
point -that  the  original  theoretical  shape  is  almost  or  entirely  lost, 
the  apparently  roundabout  process  is  not  in  vain,  for  we  are  in  per- 
fect control  of  our  design.  We  know  exactly  what  it  has  to  take  in 
the  way  of  forces,  blows  and  vibrations.  We  know  what  its  ideal 
shape  should  be.  We  know  where  we  can  practically  modify  its 
form  without  weakening  it  excessively  or  adding  excess  of  material. 
In  other  words  we  know  all  about  it,  and  therefore  know  exactly 
what  we  can  do  with  it  ;  and  whether  it  follows  in  its  shape  the 
outline  that  pure  theory  gives  it  or  some  other  outline,  it  is  never- 
theless well  designed. 

O 

"Reversed"  machine  design,  as  described  above,  based  on 
observation  and  experiment  with  regard  to  machines  already  in 
operation,  is  just  as  impossible  without  exact  analysis  and  theory 
as  is  original  design  based  merely  on  mechanical  ideas  in  the 
abstract.  The  method  once  learned  and  made  a  habit  of  mind 
will  produce  results  with  equal  facility  in  either  case,  and  results 
are  what  the  mechanical  world  is  seeking. 

Another  point  worth  noting  in  the  progress  of  the  problem 
as  given  is  the  absolute  necessity  of  possessing  some  knowlege  of 
Mechanics.  The  more  of  this  subject  the  designer  can  have  at 
his  finger  ends,  the  more  ready  and  successful  will  he  be  in  all 
problems  of  Machine  Design.  However,  the  principles  of  forces 
and  moments  clearly  understood,  and  the  application  of  the  same 
in  the  all-important  subject,  "Strength  of  Beams,"  constitute  a 
fund  of  information  that  will  give  a  splendid  start  and  a  good 
working  basis  for  simple  designs.  It  should  always  be  remem- 
bered that  a  complicated  design  is  little  more  than  a  combination 
of  simple  designs,  and  if  one  has  the  ability  to  dissect  and  analyze 
what  seems  at  first  like  a  bewildering  maze  of  parts,  complication 
is  speedily  changed  to  simplicity. 

Common  sense  goes  a  long  way  in  good  designing.  There  is 
QOthing  mysterious  about  the  process  If  the  beginner  will  only 


73 


62  MACHINE  DESIGN 

avoid  doing  things  that  are  foolish  and  ridiculous  on  their  very 
face,  if  he  will  exercise  the  same  judgment  that  he  uses  in  the 
daily  affairs  of  his  life  and  will  mix  in  something  of  mechanics  and 
mechanical  method,  he  will  be  on  the  direct  road  to  success  in  the 
art. 

Good  drawing  is  an  essential  element  of  good  design,  and  it 
is  especially  urged  that  the  sketches  and  drawings  as  reproduced 
in  the  preceding  text  be  studied  with  this  in  mind.  By  a  good 
drawing  is  meant  not  a  showy  piece  of  work,  finely  shaded  or 
artistically  lettered,  but  an  exact  layout,  definite  and  measurable, 
L'orrectly  dimensioned  if  in  detail,  and  meaning  exactly  what  it 
says.  Machine  design  is  an  exact  science,  and  the  designer  can- 
not shirk  responsibility  by  permitting  his  work  to  be  shiftless  and 
loose.  If  he  cannot  delineate  clearly  and  in  definite  form  what  he 
determines  in  his  mind  the  structure  should  be,  then  it  is  purely 
good  luck  if  he  achieves  success,  and  it  may  safely  be  asserted  that 
the  success  is  due  to  some  subsequent  care  and  finished  design 
added  to  his  feeble  effort,  rather  than  to  any  expertness  of  his  own. 
Such  success  is  of  a  very  doubtful  nature,  and  if  not  bordering  on 
financial  loss  it  is  at  least  secured  only  at  a  low  working  efficiency. 

As  examples  of  good  drawings  the  plates  shown  are  not 
claimed  to  be  anything  extraordinary,  but  it  will  be  noted  that  they 
are  clean-cut  and  definite,  and  that  even  the  sketches  are  unmis- 
takable as  to  that  which  they  are  intended  to  illustrate.  The 
information  as  to  the  design  is  all  there;  nothing  is  left  to  the 
imagination. 

Classification  of  Machinery.  It  is  intended  to  be  made  clear 
in  all  that  has  preceded,  that  the  same  method  of  attack  and  pro- 
cedure may  be  applied  to  the  designing  of  machinery,  whatever 
may  be  the  class  or  kind.  This  is  a  fundamental  principle. 
\\  hen  it  is  logically  carried  cut,  however,  it  produces  very  differ- 
ent results,  as  is  evidenced  by  the  characteristics  of  style  peculiar 
to  each  of  the  classes  of  machinery  to  one  or  another  of  which 
all  machines  belong. 

For  example,  an  engine  lathe  has  a  style  similar  to  a  di  ill 
press,  or  a  boring  mill,  or  a  screw  machine,  or  a  milling  machine. 
It  is  very  different,  however,  from  the  style  of  a  steam  engine,  or 
a  pump,  or  an  air  compressor,  or  a  locomotive;  it  is  still  more  dif- 


74 


MACHINE  DESIGN  63 

ferent  from  the  style  of  a  rolling  mill,  or  a  link  belt  conveyor,  or 
a  coal  crusher,  or  a  stamp  mill. 

These  classes  of  machinery  are  so  distinctly  marked  that  the 
novice  is  easily  able  to  perceive  that  there  is  some  controlling 
influence  in  each  which  marks  its  peculiar  style.  He  should  at 
the  same  time  see  that  the  very  analysis  that  has  been  so  strongly 
insisted  upon  in  these  pages  is  the  direct  cause  of  the  marked 
characteristic  in  design.  Each  class  of  machinery  must  satisfy 
certain  exacting  conditions  different  from  those  of  any  other,  and 
it  is  the  careful  study  of  these  conditions,  as  fundamentally 
enforced,  which  leads  to  the  strictly  logical  design. 

A  few  of  the  most  common  classes  are  enumerated  below, 
and  their  prominent  features  noted.  It  is  hoped  that  a  study  of 
them  will  familiarize  the  student  in  a  general  way  with  the 
requirements  of  each,  and  serve  as  a  guide  to  a  more  comprehen- 
sive study  of  their  detail  design  than  is  possible  in  these  pages. 

Machine  Tools.  Examples: — lathe,  planer,  milling  machine, 
drill  press,  screw  machine,  boring  mill,  grinding  machine,  etc.,  etc. 

The  machines  of  this  class  are  all  utilized  for  the  finishing  of 
metal  surfaces.  They  are  really  at  the  root  of  the  production  of 
machinery  of  all  other  classes.  Accuracy  is  their  prime  character- 
istic— accuracy  of  construction,  accuracy  of  operation,  accuracy  of 
adjustment.  Any  inaccuracy  that  exists  primarily  in  a  machine 
tool  is  reproduced  in  every  piece  upon  which  it  produces  a  finished 
surface  ;  and  since  the  mere  act  of  finishing  a  surface  upon  any- 
thing implies  that  a  rough  and  inaccurate  surface  will  not  answer, 
the  tool  then  fails  of  its  purpose  if  it  cannot  produce  a  true  sur- 
face: it  does  not  accomplish  that  for  which  it  was  designed. 

The  effect  that  this  element  of  accuracy  has  upon  the  design 
of  a  machine  tool  is  to  require  long  bearings,  convenient  and  exact 
methods  of  adjustment,  stiffness,  excess  of  material  to  absorb 
vibration,  special  shapes  to  facilitate  application  of  jigs,  fixtures, 
and  exact  manufacturing  devices  insuring  interchangeabilit^  of 
parts,  dust  guards,  and  automatic  lubrication. 

Machine  tools  are  essentially  machines  of  maximum  output, 
and  depend  for  their  success,  not  only  upon  their  accuracy  as 
noted,  but  also  upon  their  ability  to  do  the  greatest  amount  of  work 
per  square  foot  of  space  occupied,  with  the  least  amount  of  manual 


75 


64  MACHINE  DESIGN 


labor  and  attention  on  the  part  of  the  operator.  This  is  especially 
true  of  automatic  machinery,  which  perhaps  might  be  classed  by 
itself  in  this  respect,  but  which  is  nevertheless  included  under  the 
broad  term  of  a  machine  for  producing  finished  surfaces,  being 
merely  the  highest  and  most  refined  form  of  same.  For  machines 
of  this  class  the  designer  has  to  study  every  detail  with  the  most 
minute  attention,  packing  away  the  operating  parts  into  the 
smallest  space  and  yet  providing  ready  means  for  access,  removal, 
and  repair.  Clearances  that  would  be  too  little  for  other  kinds  of 
machinery  are  permitted  and  provided  for;  material  of  high  grade, 
strength,  and  wearing  quality,  though  expensive  in  first  cost,  and 
requiring  the  most  expert  skill  to  finish  and  to  fit  into  place,  must 
be  used  in  order  to  keep  the  machine  compact  and  yet  of  large 
capacity,  to  make  it  reasonably  light  in  weight  and  yet  amply 
strong. 

Another  point  which  has  a  great  influence  on  the  design  of  a 
machine  tool  is  that  we  can  never  tell  in  advance  just  what  it  will 
have  to  stand  in  work,  for  the  variation  in  the  material  that  it  fin- 
ishes, the  uncertain  skill  of  the  operator  who  runs  it,  the  crowding 
to  its  limit  of  capacity  and  even  beyond  in  times  of  press  of  business, 
and  the  many  other  stresses  that  may  suddenly  and  without  warn- 
ing be  thrown  upon  it.  must  all  be  thought  of  and  provided  for. 

The  points  above  mentioned  are  but  a  few  of  those  which  the 
designer  of  machine  tools  has  to  meet,  and  are  presented  merely 
as  illustrations  to  show  the  special  skill  required  in  this  class  of 
machinery.  It  is  readily  seen  that  while  the  machine  tool 
designer  has  great  latitude  in  choice  of  material  and  in  expendi- 
ture of  money  for  refinement  of  structure — perhaps  greater  lati- 
tude than  in  any  other  class,  yet  he  is  held  down  as  in  no  other 
to  the.  final  productive  results,  a  small  percentage  of  failure  entirely 
throwing  out  the  machine  as  a  marketable  product. 

The  style  and  external  appearance  of  machine  tools  have  a 
character  of  their  own  resulting  from  this  extreme  detailed  care  in 
design.  Corners  and  fillets  are  carefully  rounded;  surfaces  and 
intersections  are  definitely  made;  in  short,  the  mechanical  beauty 
of  a  machine  tool  is  seen  only  from  a  near  view  and  close  inspec- 
tion, and  it  is  to  this  end  that  the  design  is  constantly  directed 
Appearance  is  a  large  factor  in  the  sale  of  a  fine  tool,  and  the 


76 


MACHINE  DESIGN  65 


prestige  of  the  American  trade  abroad  in  this  respect  is  very 
noticeable. 

Motive=Power  flachinery.  Examples: — Steam  engine,  gas 
engine,  air  compressor,  steam  pump,  hydraulic  machinery,  etc.,  etc. 

The  element  of  heat  enters  into  the  design  of  all  machinery 
in  this  class.  The  natural  agents,  air,  gas,  and  water,  in  their 
various  forms,  are  taken  into  the  machine  in  the  most  efficient 
form  in  which  it  is  possible  to  obtain  them,  are  robbed  of  their 
energy  to  provide  power,  and  are  discharged  in  a  form  as  weak 
and  inert  as  the  efficiency  of  the  machine  will  determine. 

In  contrast  to  the  class  of  machinery  just  studied,  it  should 
be  noted  that  these  machines  do  not  produce  any  material  thing; 
that  is,  they  do  not  produce  finished  surfaces  on  metals,  make 
screws  or  bolts,  bore  holes  in  castings,  or  turn  line  shafting. 
They  merely  take  the  energy  of  the  natural  agent,  which  is  not  in 
a  form  available  for  use,  and  transform  it  into  motive  power  for 
general  use. 

Hence  the  element  of  accuracy  as  entering  into  the  design  of 
these  machines  is  necessary  only  for  their  own  efficient  operation, 
and  not  for  the  quality  of  the  thing  which  they  produce,  as  in  the 
case  of  machine  tools.  For  example,  the  power  furnished  by  one 
steam  engine  to  drive  a  line  shaft  is  as  good  as  that  of  another  as 
far  as  the  rotating  of  the  shaft  is  concerned,  provided,  of  course, 
that  both  are  equipped  with  the  same  quality  of  governing  mechan- 
ism. The  fact  that  one  of  the  engines  has  a  good  adjusting  device 
on  the  main  bearing  while  the  other  has  not  is  of  no  consequence 
from  the  standpoint  of  the-  line  shaft,  but  it  is,  of  course,  of  con- 
sequence respecting  the  efficient  operation  of  the  engines. 

The  design  of  steam  engines  and  similar  machines  is  of  a 
rough  nature  compared  with  that  of  machine  tools,  as  far  as  the 
detail  of  surface  is  concerned.  General  accuracy  is  nevertheless 
essential  for  the  machine's  own  sake,  but  while  in  the  machine 
tool  we  deal  with  thousandths  of  an  inch,  in  the  steam  engine 
hundredths  of  an  inch  indicates  fine  work. 

These  machines  are  subject  to  extremes  of  temperature  that 
have  to  be  provided  for  in  the  design  and  arrangement  of  the  parts. 
Being  prime  movers,  controlling  the  operation  of  many  machines, 
they  must  be  certain  to  run  during  their  period  of  work;  hence 


77 


66  MACHINE  DESIGN 


design  and  adjustment  must  be  positive,  and  when  the  latter  can- 
not  be  made  while  running,  it  must  be  quickly  and  definitely  accom- 
plished when  a  stop  is  made.  Simplicity  of  construction  is  essential, 
facilitating  cheap  and  quick  repairs.  The  design  should  be  such 
that  constant  attention  while  running  is  avoided,  the  usual  atten- 
tion of  the  engineer  being  a  safeguard  rather  than  an  implied  fac- 
tor of  the  original  design.  General  rigidity  and  stiffness  are 
important,  also  good  balancing  of  the  moving  parts,  and  weight  for 
absorption  of  vibration;  otherwise  under  the  constant  daily  run  the 
machines  will  tear  to  pieces  not  only  themselves  but  their  founda- 
tions. 

As  far  as  external  appearance  goes  in  -this  and  subsequent 
classes  to  be  mentioned  we  are  on  a  very  different  basis  from  that 
of  machine  tools.  General  mechanical  symmetry  of  form  is  aimed 
at  in  the  design,  and  the  several  smaller  parts  depend  for  their  out- 
line (aside  from  considerations  of  strength,  which  are,  of  course, 
always  in  order)  upon  the  harmonious  relation  which  they  bear  to 
the  main  and  fundamental  elements  of  the  machine.  Such 
machinery  as  air  compressors,  steam  encrines.  pumps,  and  the  like 
are  viewed  as  a  whole,  and  criticised,  not  detail  by  detail,  as  is  the 
machine  tool,  but  as  to  general  effect  of  outline  observed  from 
some  distance.  To  convey  the  desired  effect  to  the  eye  the  desio-n 

«.  *.  C1 

must  be  bold  and  massive,  connections  simple  and  direct,  and  the 
smaller  parts  must  not  be  so  dwarfed  in  size  as  to  appear  like  deli- 
cate ornaments  instead  of  integral  parts  of  the  machine.  The  lines 
of  connected  parts  must  be  continuous  from  one  part  to  the  other; 
and  when  interrupted  by  flanges,  bosses,  or  lugs,  the  latter,  which 
are  merely  incidental  to  the  former  must  not  be  allowed  to  obscure 
wholly  the  main  lines  of  the  fundamental  pieces. 

It  is  attention  to  such  points  as  thes°  that  marks  the  difference 
between  well-designed  motive-power  n.cu.hinery  and  that  of  the 
opposite  character.  Even  though  the  little  details  of  fillets  and 
corners  and  surfaces  may  have  their  effect  from  a  close  point  of 
view,  the  design  will  stand  or  fall  in  excellence  on  its  bolder 
features,  as  noted  above. 

Structural  Machinery.  Examples: — Hoists,  cranes, elevators, 
transfer  tables,  locomotives,  cars,  conveyors,  cable-ways,  etc.,  etc. 

In  the  two  preceding  classes  that  have  been  noted,  cast  iron 


78 


MACHINE  DESIGN  67 

in  the  form  of  foundry  castings  enters  as  the  principal  material. 
Steel  is  utilized  for  shafts,  studs,  pins,  and  keys.  Also  special 
forgings,  malleable  iron  and  steel  castings  enter  as  factors  in  the 
production  of  the  machinery  discussed.  Foundry  castings,  how- 
-ever,  compose  the  great  body  of  the  material  used,  and  the  chief 
problems  involved  are  those  of  the  expert  moulding  of  cast  iron, 
and  the  handling  and  finishing  of  the  same.  For  the  operating 
parts,  steel  of  fine  grade  is  used  in  highly  finished  form,  expens- 
ive because  of  its  fineness,  and  yet  a  necessity  to  the  extent  it  is 
used.  Brass  and  bronze  are  used  in  the  same  way,  generally  in 
connection  with  the  bearings  for  the  shafts. 

O 

Structural  machinery,  on  the  contrary,  uses  steel  as  the  basis 
of  its  construction.  The  fundamental  structure  is  built  up  of 
plates,  channels,  beams,  and  angles;  castings,  though  numerous, 
are  relatively  small,  being  riveted  or  bolted  to  the  main  structure 
and  controlled  in  their  design  by  its  requirements. 

Steel  is  used  in  this  manner  partly  because  the  exclusive  use 
of  castings  is  prohibited  on  account  of  the  excessive  weight,  and 
therefore  expense,  and  partly  because  castings  could  not  be  made 
which  would  possess  the  necessary  toughness  and  strength.  In 
many  cases  the  size  of  the  machinery  is  such  that  castings,  even 
if  they  could  be  made,  would  not  support  their  own  weight. 
Moreover,  machinery  of  this  class  is  subjected  to  rough  service, 
and  yet  must  be  practically  infallible  under  all  conditions,  neither 
being  uncertain  in  operation  at  critical  moments  nor  entirely  fail- 
ing under  an  extraordinary  load. 

The  design  of  structural  machinery  is  tied  up  to  con- 
ditions existing  largely  outside  of,  the  locality  in  which  the  ma- 
chinery is  built.  The  steel  plates  and  structural  shapes  required, 
being  products  of  the  rolling  mill,  have  to  conform  to  the  latter's 
standards.  The  rivets,  bolts  and  other  fastenings  have  to  be  in 
accordance  with  the  established  practice  of  the  structural  iron 
worker,  in  order  to.  permit  punching,  shearing  and  bending  ma- 
chinery of  regular  form  to  be  utilized.  Shipment  on  standard 
railway  cars  has  to  be  considered,  the  design  often  requiring  to  be 
modified  to  permit  this  and  nevertheless  insure  positive  and 
accurate  assembling  in  the  field. 

Steel  castings,  both  large  and  small,  find  ready  application  in 


68  MACHINE  DESIGN 

this  class  of  work;  also  steel  forcings,  requiring  to  be  worked 
under  a  heavy  hammer  and  in  many  cases  by  specially  devised 
processes. 

In  structural  design  less  of  the  actual  process  of  manufacture 
is  under  the  eye  of  the  designer  than  in  the  former  class3S  of 
machinery  which  have  been  considered,  and  hence  more  allowance 
has  to  be  made  for  things  not  coming  exactly  right  to  the  fraction 
of  an  inch.  It  would  be  bad  design  to  plan  any  structural  piece 
of  work  with  the  same  closeness  of  detail  permitted,  and  in  fact 
required,  in  the  case  of  machine  tools,  or  even  in  the  case  of  motive- 
power  machinery.  In  planning  structural  work  the  idea  must  be 
carried  out,  of  certainty  of  operation  in  spite  of  roughness  of  detail 
and  variations  of  construction.  This  does  not  necessarily  imply 
inaccuracy,  or  shiftless,  loosely  constructed  machinery;  on  the  con- 
trary, quite  the  reverse.  The  locomotive,  for  example,  is  one  of 
the  most  refined  pieces  of  mechanism  that  exists  today;  and  yet 
the  methods  applied  to  the  construction  of  machine  tools  would 
prove  a  failure  on  the  locomotive.  The  design  of  a  car  axle  box 
has  to  be  just  right  else  it  will  heat  and  destroy  itself;  the  same  is 
true  of  the  spindle  of  a  fine  engine  lathe;  and  yet  how  rough  the 
former  is  compared  with  the  latter,  and  how  unsuited  either  would 
be  for  use  on  the  service  of  the  other. 

As  a  general  rule  structural  machinery  can  be  more  closely 
proportioned  to  theoretically  calculated  size  than  can  the  preceding 
types.  The  rolled  material  of  which  it  is  made  is  of  a  uniform 
and  homogeneous  nature  owing  to  its  process  of  manufacture, 
hence  its  every  fibre  may  be  counted  on  to  sustain  its  share  of  the 
total  load  imposed  upon  it.  This  is  in  sharp  contrast  to  the  case 
of  cast  iron,  which  is  of  such  a  porous  and  irregular  structure  that 
we  have  to  use  a  large  factor  of  safety  to  cover  this  inherent 
defect. 

Steel  castings  of  both  small  and  large  size  (which  are  quite 
apt  to  be  utilized  in  this  class  of  machinery  for  parts  that  can  with 
difficulty  be  made  out  of  rolled  material),  if  properly  designed  of 
uniform  thickness,  with  all  corners  well  filleted  and  with  the 
channels  for  the  flow  of  the  molten  metal  direct  and  ample,  are 
nearly  as  reliable  as  rolled  steel.  In  parts  subject  to  excessive 
vibration,  shocks,  and  sudden  wrenchings,  as,  for  example,  the 


80 


MACHINE  DESIGN  69 

side  frames  or  the  connecting  rod  of  a  locomotive,  the  forged  and 
hammered  material  is  practically  a  necessity.  This  is  especially 
the  case  when  the  possible  breakage  of  the  part  would  cause 
serious  consequences  involving  heavy  loss  of  life  and  property. 

From  the  several  points  of  view  as  above  considered,  it  can 
be  readily  appreciated  that,  while  structural  work  is  in  one  sense 
rough  and  unpolished,  yet  it  requires,  from  an  engineering  stand- 
point, quite  as  much  breadth  of  experience  and  judgment  as  any 
of  the  other  types.  The  fine-tool  designer,  least  of  all,  perhaps, 
requires  book  theory,  but  does  require  an  extended  machine-shop 
experience.  The  designer  of  motive-power  machinery  needs  pure 
physical  theory  and  shop  experience  of  a  large  and  broad  scope. 
The  structural  designer  is  least  of  all  concerned  with  refined  and 
minute  finishing  processes,  but  utilizes  his  theory  absolutely,  even 
though  roughly. 

Mill  and  Plant  Machinery.  Examples : —  Rolling  mills, 
mining  machinery,  crushers,  stamps,  rock  drills,  coal  cutters,  the 
machinery  of  blast  furnaces  and  steel  mills,  tube  mills,  etc*.,  etc. 

This  machinery  constitutes  a  class  which  in  the  roughness 
of  its  operation  exceeds  all  others.  Moreover,  it  is  machinery 
which  for  the  most  part  is  in  continuous  operation — 24  hours  per 
day  and  365  days  in  the  year.  Hence  refinement,  even  such  as 
might  be  permitted  in  the  preceding  class  of  Structural  Machinery, 
would  be  fatal  here.  The  conditions  that  surround  plant  machinery 
are  unfavorable  in  the  extreme  to  the  life  of  any  material  or  metal, 
and  it  is  not  possible  to  change  these  conditions  or  give  more 
than  partial  protection  to  the  operating  parts.  Hence  the  design 
of  such  machinery  must  proceed  primarily  on  the  assumption 
that  abuse  and  neglect,  grinding  away  of  surfaces,  chemical  eating 
away  of  metal,  flooding  of  parts  with  water  gritty  "and  corrosive, 
subjection  to  sudden  bursts  of  flame  and  intense  heat,  etc.,  will 
in  a  relatively  short  time  totally  destroy,  perhaps,  the  entire 
structure. 

In  view  of  the  continuous  nature  of  the  working  process, 
which  must  be  kept  up  in  spite  of  these  almost  insurmountable 
conditions,  the  problem  in  each  case  becomes  one  of  expediency; 
and  the  designs  and  arrangement  of  machinery  must  be  so  worked 
out  that  operation,  repair,  construction,  and  installation  can  all  go 


81 


70  MACHINE  DESIGN 

on  simultaneously  without  stopping  the  continuous  process,  and 
with  but  a  small  degree  of  inconvenience  to  the  operation  of  the 
plant. 

This  problem,  difficult  though  it  may  seem,  can  be  worked 
out  successfully,  as  is  evidenced  by  the  great  number  of  plants  of 
the  continuous  character  operating  at  high  efficiency  throughout 
the  world.  The  engineering  and  designing  skill  required  to  ac- 
complish this,  is  perhaps  of  the  highest  degree  met  with  in  mod- 
ern practice,  for  in  it  is  involved  a  working  knowledge  of  the 
possibilities,  if  not  the  detailed  designs  of  machinery  included  in 
all  classes.  And  yet,  as  in  the  most  elementary  case  of  simple 
design  that  can  be  conceived,  the  result  is  accomplished  in  the 
same  way,  namely,  by  studying  the  conditions  (analysis),  devel- 
oping an  ideal  application  to  those  conditions  (theory),  and  then 
reducing  the  ideal  design  to  a  practical  basis  (modification). 

A  Few  Pointed  Suggestions  on  Original  Design.  Original 
design  deals  with  the  development  of  original  mechanical  ideas. 
The  JO'S  me  requisite  for  the  development  of  an  idea  is  to  under- 
stand thoroughly  the  idea  in  the  rough.  See  distinctly  the  mark 
aimed  at,  and  never  lose  sight  of  it.  If  a  method  of  reaching  it 
is  already  outlined,  understand  that  also  thoroughly  and  the  prin- 
ciples involved.  It  is  impossible  to  go  ahead  blindly  and  hope  to 
come  out  right.  No  good  machine  was  ever  built  that  does  not 
stand  for  hours  of  concentrated  thought  on  the  part  of  its  designer. 
Good  machines  never  lift.pper,,  they  always  yrow. 

Just  as  soon  as  the  object  to  be  accomplished  is  clearly  under- 
stood, begin  to  produce  some  visible  work  on  the  problem.  Sketch 
something.  Get  some  ideas  on  paper.  Ideas  on  paper  suggest 
other  ideas.  If  the  problem,  for  example,  is  one  of  lathe 
design,  sketch  a  rectangle,  and  call  it  the  headstock;  another  rec- 
tangle, and  call  it  the  footstock;  a  couple  of  scratches  for  the 
centers;  some  steps  for  the  cone  pulley;  three  or  four  lines:  for  the 
bed';  and  as  many  more  for  the  supports.  There  is  now  something 
on  paper  to  look  at;  the  design  is  begun. 

It  is  much  better  to  stare  at  this  sketch,  than  into  blank 
space  trying  to  imagine  the  finished  design.  No  matter  how  rough 
the  sketch  may  be,  a  short  study  of  it  will  develop  some  limitino- 
conditions  that  before  were  not  apparent.  Guess  at  a  few  rough 


82 


MACHINE  DESIGN  71 


dimensions;  put  them  on  the  sketch;  develop  another  view— a  plan 
or  a  side  elevation — all  still  in  the  roughest  style,  without  any 
regard  to  finished  detail.  Information  will  be  growing  all  the 
while,  and  the  problem  will  be  opening  up.  At  this  stage  it  is 
probable  that  the  sketch  can  easily  be  seen  to  be  wrong  in  many 
respects.  Perhaps  the  arrangement  will  not  do  at  all. 

This  is  a  good  sign..  It  showrs  that  the  design  is  progressing. 
It  is  a  valuable  thing  to  know  that  certain  plans  cannot  be  fol- 
lowed. Do  Dot  rub  out  part  of  the  sketch  already  made  and  try 
to  remedy  it.  Begin  again.  Make  another  sketch.  Sketch  paper 
is  cheap.  By  and  by  it  may  prove  to  be  very  desirable  to  have 
that  first  rough  outline  available  for  comparison;  or  it  may  be  that 
some  of  its  ideas  can  be  applied  on  other  sketches.  The  second 
sketch  may  "show  up"  little  or  no  better  than  the  first.  Make 
another,  and  another,  and  another,  until  the  subject  is  thoroughly 
digested.  It  is  wonderful  how  helpful  it  is  to  have  some  marks 
on  paper  relative  to  a  design,  even  though  they  be  of  the  utmost 
crudeness.  They  save  imaginative  power  tremendously;. and,  even 
with  them,  all  available  powers  of  imagination  will  be  needed 
before  the  design  is  perfected. 

A  careful  comparison  of  one's  sketches,  rejecting  here,  and 
approving  there,  will,  little  by  little,  bring  about  a  definite  opinion, 
and  the  scale  drawing  can  be  begun. 

As  in  the  case  of  the  first  sketch,  so  in  the  case  of  the  first 
scale  drawing,  get  some  lines  on  paper  as  quickly  as  possible. 
Draw  something,  even  if  it  is  nothing  more  than  a  straight  hori- 
zontal line.  Do  not  stare  at  blank  paper  for  an  hour  trying  to 
imagine  how  the  tenth  or  eleventh  line  is  going  to  be  drawn  in 
relation  to  the  first  line.  .Do  not  worry  about  the  later  lines 
until  it  is  time  for  them  Draw  the  first  line  at  once;  and,  when 
the  second  line  is  drawn,  if  the  first  line  proves  to  be  wrong, 
make  it  right.  As  in  the  rough  sketch,  that  first  horizontal  line 
is  an  immense  relief  from  the  great  waste  of  blank  paper  of  a 
fresh  sheet.  It  is  something  to  look  at.  It  is  the  beginning  of  a 
detailed  design.  If  it  happens  not  to  be  the  absolutely  correct 
foundation  to  build  upon,  it  at  least  is  something  to  tear  down. 
The  main  purpose  of  these  preliminary  drawings  is  to  keep  the 
mind  active  on  the  problem;  and  advance  toward  the  final  accom- 


83 


MACHINE  DESIGN 


plisbment  of  the  design  is  often  made  quite  as  rapidly  by  discover- 
ing  what  to  tear  down  as  by  consistently  building  up. 

.  AVhen  a  detail  draftsman  who  has  been  used  to  having  all  his 
work  laid  out  for  him  by  an  expert  designer  attempts  to  take  up 
original  work  for  himself,  he  encounters  the  drawing  of  that  first 
line  in  a  way  he  never  did  before.  He  is  apt  to  worry  for  some 
time  over  the  possible  or  impossible  results  of  drawing  that  first 
line.  If  he  continue  this,  he  will  be  sure  to  fail.  The  second  line 
is  much  easier  to  draw  than  the  first,  and  the  third  than  the  second; 
and  the  next  hundred  will  follow  on  in  comparatively  smooth 
sequence,  all  because  of  bold  action  on  the  first  few  lines. 

And  yet.  just  as  the  design  appears  to  be  progressing  smoothly, 
and  the  advanced  progress  of  the  drawing  seems  cause  for  congratu- 
lation, careful  consideration  may  disclose  a  "-snag"  not  previously 
known  to  exist  in  the  problem.  Further  study  pursued  along 
the  line  of  this  new  discovery  may  show  that  the  whole  layout 
thus  far  has  been  radically  wrong,  and  that  a  fresh  start  will  have 
to  be  made.  At  such  a  time  the  young  designer  is  apt  to  feel 
that  his  labor  has  all  been  thrown  away,  and  he  becomes  discour- 
aged. There  is,  however,  no  cause  for  discouragement.  Machine 
Design  might  almost  be  defined  to  be  the  ••successful  elimination 
of  snags."  It  takes  some  ability  to  discover  an  obstacle  of  this 
sort;  to  know  a  ••snag"'  when  an  opportunity  to  see  it  is  given. 
It  takes  a  good  designer  to  eliminate  such  a  difficulty  after  it  has 
been  found.  If  there  were  no  ••snags"''  it  would  not  require  great 
ability  to  design  machines.  M-any  machines  fail  because  in  them 
there  are  a  lot  of  undiscovered  -snags."  .  Others  fail  because  the 
'•snags."  although  discovered,  were  not  eliminated  by  careful  design. 
Do  not  be  afraid  to  make  a  lot  of  "first"  drawings.  It  is 
just  as  important  to  digest  the  design  thoroughly  by  means  of 
scale  drawings,  as  it  was  to  digest  it  originally  by  means  of 
the  rough  sketches.  An  attempt  to  make  the  first  drawing  of  an 
original  design  absolutely  right  would,  it  is  safe  to  say,  produce  a 
poor  design,  one  that  could  be  much  improved  by  further  trial. 
Let  the  drawings  multiply,  one  after  another,  until  the  final  one 
is  reached,  in  which  the  perfection  of  detail  will  eliminate  all  the 
bad  points  of  the  preceding  drafts  and  incorporate  good  ones  of  its 
own  based  on  the  study  of  the  others. 


84 


MACHINE  DESIGN  73  , 


And  yet  it  is  often  true  that  the  first  design  laid  out,  even 
after  many  others  have  been  developed,  may  be  found  to  possess 
features  that  render  a  return  to  it  desirable.  This  is  why  it  is 
always  better  to  produce  a  collection  of  designs  than  to  attempt 
to  rub  out  and  work  over  the  first  one.  The  best  designers  usually 
have  a  great  number  of  sketches  showing  how  to  accomplish  a 
single  result.  Likewise,  they  also  have  a  series  of  layouts  to  scales 
showing  in  detailed  form  the  development  of  their  various  ideas. 
This  is  because,  without  a  careful  consideration  of  many  methods^ 
they  themselves  feel  incompetent  to  judge  of  the  best  design  pos- 
sible for  accomplishing  a  given  result. 

Sketches  and  original  designs  should  always  be  dated  and 
signed.  Different  designers  may  be  working  on  the  same  prob- 
lem, and  priority  of  design  will  never  be  allowed  except  upon 
signed  and  witnessed  papers.  It  is  embarrassing  to  find,  after 
months  and  perhaps  years  have  passed  since  an  original  drawing 
was  made,  that  one's  rights  have  been  preempted  merely  because 
there  was  no  date  or  signature  to  define  them. 

In  redesigning  or  modifying  an  existing  machine,  never  make 
a  change  merely  for  the  sake  of  doing  so.  Give  the  good  points  of 
the  machine  a,  chance,  and  devote  attention  in  the  new  design  to 
correcting  the  bad  points.  It  is  in  bad  taste,  if  it  be  not  actually 
childish,  to  "look  wise  and  suggest  a  change"  in  details  which 
happen  to  have  been  designed  by  another  party,  but  which,  never- 
theless, are  by  common  engineering  judgment  pronounced  good 
for  the  special  work  intended.  This  element  of  unfair  and  selfish 
criticism  has  more  than  a  moral  bearing.  When  it  is  carried  into 
the  superintendence  of  designing  work,  it  extinguishes  the  person- 
ality of  the  subordinate  draftsman;  his  efficiency  as  an  original 
thinker  is  lowered;  and  narrow  designs  are  produced. 

"The  best  way  for  a  subordinate  to  dispose  of  what 
appears  to  be  a  poor  suggestion  from  a  superior,  is  to  work  it  out 
to  the  best  degree  possible."  If  it  turns  out  to  be  good  the 
credit  of  working  it  out  belongs  to  the  man  who  did  it.  If  it  is 
actually  bad,  a  careful  working  out  will  usually  develop  the  fact 
beyond  dispute,  and  save  unprofitable  argument.  For  the  success 
or  failure  of-  a  machine  there  is  only  one  argument  better  than 
the  detail  drawings,  and  that  is  the  machine  itself  in  operation. 


85 


74  MACHINE  DESIGN 


Detail  drawings,  however,  are  infinitely  better  prosecutors  or 
defendants  than  u  multitude  of  wordy  counsel. 

Summary.  The  above  classification  of  machinery  might  be 
subdivided  and  extended  indefinitely,  and  on  the  broad  basis  on 
which  it  is  given  it  doubtless  does  not  cover  the  entire  field.  As 
an  illustration,  however,  not  only  of  types  of  machinery,  but  of 
methdlls  of  design  and  study,  it  is  hoped  that  it  may  be  of  assist- 
ance in  giving  a  start  to  the  student  of  machine  design,  in  what- 
ever class  his  interests  may  happen  to  lie. 

It  is  the  general  principles  of  the  art  which  it  is  important  to 
master.  It  is  not  the  designing  of  a  locomotive,  or  a  stationary 
steam  engine,  or  a  crane,  or  an  engine  lathe,  or  a  rolling  mill, 
which  should  be  sought  to  be  learned,  but  the  designing  of  any- 
tliiittj  that  may  confront  us.  Specializing  is  sure  to  come  to  the 
designer  in  the  course  of  his  experience,  and  when  it  does  he  merely 
fits  to  the  particular  specialty  the  principles  he  knows  for  all,  and 
practically  develops  them  along  that  individual  line. 


86 


MACHINE  DESIGN, 

PART  II. 


Introduction.  In  Part  I  is  illustrated  a  definite  and  systematic  method 
of  attacking  the  design  of  a  machine  as  a  whole.  In  Part  II  the  same  plan  is 
followed  with  regard  to  the  detail  of  its  component  parts,  the  machine  ele- 
ments which  are  chosen  as  illustrations  of  the  method,  being  the  simplest  and 
most  familiar  forms  in  common  use.  - 

As  before,  the  student  must  strive  to  grasp  and  absorb  the  method  of  design 
rather  than  any  specific  and  established  form  of  a  machine  part.  Part  II  is 
not  a  compendium  of  design,  does  not  attempt  to  be  complete  or  exhaustive  in 
any  of  its  chapters,  but  is  condensed  and  simplified  in  order  to  lead  the 
student  into  systematic  mechanical  thinking  and  logical  and  definite  action. 
Each  chapter  is  intended  to  stimulate  to  further  and  more  exhaustive  study 
along  lines  broader  than,  and  under  conditions  different  from  those  that  can 
be  specified  in  a  general  discussion.  But  no  matter  how  deeply  investigation 
may  be  carried,  or  how  specialized  the  study  may  become,  the  student  must 
real:ze  that  his  path  of  action  in  any  case  whatsoever  must  lie  along  the 
lines  of  Analysis,  Theory,  and  Practical  Modification  systematically  applied. 


BELTS. 

NOTATION— The  following  notation  is  used  throughout  the  chapter  on  Belts : 

A=  Sectional  area  of  belt  (square inches)  R  =  Radius  of  pulley  (feet). 

=  bh.  r  =  Radius  of  pulley  (inches). 

6= Width  of  belt  (inches).    '  T  =  Initial  tension  (Ibs.). 

F=Force  of  friction  at  pulley  rim  (Ibs.).  Tn=Total  tension  on  tight  side  (Ibs.). 

h  =Thickness  of  belt  (inches)  T0=Total  tension  on  slack  side  (Ibs.). 

^-Coefficient of  friction.  t    -  Working  tension  of  belt    (Ibs.  per 
N=Number of  revolutions  of  pulley  per  square  inch). 

minute.  V  = Velocity  of  belt  (feet  per  minute). 

71  =Fractionof  circumference  of  pulley  w  -Weight  of  belt  per  cubic  inch  (Ibs.). 

embraced  by  belt.  z    =  Factor  due  to  centrifugal  force. 
P=Driving  force  at  pulley  rim  (lbs.)=F. 

ANALYSIS.  When  a  belt  is  stretched  over  a  pair  of  pulleys, 
is  cut  off  at  the  proper  length,  and  is  laced  together  into  an  end- 
less band,  it  is  evident  that  as  long  as  the  belt  is  at  rest  there  is  a 
nearly  uniform  tension  in  it  throughout  its  length,  due  to  the  tight- 
ness with  which  the  lacing  is  drawn  up.  If  the  distance  between 
the  pulleys  is  considerable,  the  weight  of  the  belt  itself  as  it  hangs 
between  the  pullftvs  will  produce  a  slightly  greater  tension  next  to 


76  MACHINE  DESIGN 


the  pulleys  than  exists  in  the  middle  of  the  span.  This  increase 
of  tension  due  to  the  weight  of  the  belt  would  make  but  little  dif- 
ference in  the  unit-stress  in  the  material  of  which  the  belt  is  made; 
hence  it  may  safely  be  assumed  that  the  tension  in  the  belt  when 
at  rest  is  uniform  throughout  its  entire  length. 

When  we  start  to  transmit  power  through  the  belt  by  turning 
one  of  the  pulleys,  thereby  driving  the  other  pulley  the  condition 
of  stress  in  the  belt  is  at  once  materially  changed.  As  the  belt  is 
a  flexible  member,  we  can  transmit  only  a  pull  to  the  other  pulley, 
thereby  turning  it  around,  the  push  which  is  at  the  same  time 
given  to  the  other  side  of  the  belt  merely  acting  to  make  the  belt 
sag  or  become  slack.  Hence  the  immediate  effect  of  starting  mo- 
tion in  a  belt  is  to  change  the  condition  of  equal  tension  through- 
out its  length,  to  that  of  unequal  tension  in  the  two  sides.  The 
driving  side  is  tight,  while  the  other  is  loose,  the  former  having 
gained  as  much  tension  as  the  latter  has  lost,  and  the  sum  of  the 
two  being  practically  equal  to  the  sum  of  the  tensions  in  the  two 
sides  of  the  belt  when  at  rest.  This  is  not  strictly  true,  as  will  be 
shown  later;  but  it  is  sufficiently  accurate  to  form  a  good  basis 
for  the  practical  design,  at  least  of  slow-speed  belts. 

This  condition  of  tight  and  slack  sides  is  made  possible  by 
the  fact  that  the  belt,  in  being  wrapped  around  the  pulleys  under 
tension,  has  friction  on  their  surfaces.  Thus,  we  can  pull  hard  on 
one  side  without  slipping  the  belt  around  the  pulleys,  but  could 
not  do  this  if  the  pulleys  were  perfectly  smooth  or  frictionless,  for 
in  that  case  the  slightest  pull  on  one  side  would  slip  the  belt 
around  the  pulleys.  In  fact,  it  would  be  impossible  to  produce 
any  pull  by  means  of  the  driving  pulley,  for  the  pulley  would 
merely  slip  around  inside  the  belt. 

The  amount  of  pull  we  can  apply  to  the  belt  is  therefore  lim- 
ited by  the  tension  at  which  the  belt  slips  around  the  pulley. 
Moreover,  since  the  force  of  friction  between  the  belt  and  pulley 
is  dependent  upon  the  normal  force  with  which  the  belt  is  pressed 
against  the  pulley,  and  the  coefficient  of  friction  between  the  two, 
it  is  evident  that  the  tighter  the  belt  is  laced  up,  and  the  rougher 
the  surfaces  of  the  pulley  and  belt,  the  greater  is  the  force  that 
can  be  transmitted  through  the  belt.  This  leads  to  the  conclusion 
that  it  would  be  possible  to  transmit  any  amount  of  power  through 


90 


RACK    CUTTING    PLANER. 


MACHINE  DESIGN  77 

any  belt  however  small,  if  the  belt  were  only  laced  ap  tight 
enough. 

This  conclusion  is  literally  true;  but  the  important  fact  now 
comes  in,  that  the  strength  of  the  material  of  which  the  belt  is 
made  is  limited,  and  while  theoretically  we  might  be  able  to  ac- 
complish the  above,  it  would  be  impossible  to  do  so  in  practice, 
for  at  a  certain  point  the  belt  would  break  under  the  strain.  Other 
practical  considerations  also  come  in,  which  fix  this  limit  of  power 
transmission  at  a  point  far  below  the  breaking  strength  of  the  ma- 
terial. 

The  complete  analysis  is  not  quite  as  simple  as  the  above,  es- 
pecially for  high-speed  belts.  When  the  driving  side  of  the  belt 
becomes  tight,  it  stretches  and  grows  longer;  and  at  the  same 
time  the  other  side  of  the  belt  becomes  slack  and  grows  shorter. 
But  it  is  not  true  that  the  increase  in  the  one  side  is  the  same  as 
the  decrease  in  the  other,  and  this  fact  produces  the  condition  that 
the  sum  of  the  tensions  in  motion  is  not  quite  the  same  as  the  sum 
of  the  tensions  at  rest. 

Again,  when  the  belt,  as  it  passes  around  the  pulley,  changes 
its  straight-line  direction  to  circular  motion,  each  particle  of  the 
belt— like  a  body  whirling  at  the  end  of  a  cord  about  a  center  of 
rotation — tends  by  centrifugal  force  to  fly  away  from  the  surface 
of  the  pulley,  thereby  decreasing  the  normal  pressure,  and  hence 
the  friction.  This  centrifugal  force  also  changes  somewhat  the 
tensions  in  the  belt'between  the  pulleys.  As  the  centrifugal  force 
increases  in  proportion  to  the  square  of  the  linear  velocity,  it  is 
evident  that  the  effect  is  greater  at  high  speeds  than  at  moderate 
or  low  speeds. 

A  further  circumstance  that  affects  the  driving  power  of  a 
belt  is  the  stiffness  of  the  leather  or  other  material  of  which  the 
belt  is  made.  As  it  passes  around  the  pulley,  the  belt  is  bent  to 
conform  to  the  circumference  of  the  pulley,  and  is.  again  straight- 
ened out  as  it  leaves  the  pulley.  Hence  the  theoretically  perfect 
action  is  modified  somewhat  according  to  the  sharpness  of  the 
bending  and  the  thickness  or  flexibility  of  the  belt;  in  other  words, 
a  small  pulley  carrying  a  thick  belt  would  be  the  worst  case  for 
successful  calculation  on  a  theoretical  basis. 

THEORY.     The  condition  of  the  tight  and   loose   sides  of  a 


91 


78 


MACHINE  DESIGN 


belt  transmitting  power,  is  similar  to  that  of  the  weighted  strap 
and  fixed  pulley  shewn  in  Fig.  17.  If  motion  is  desired  of  the 
strap  around  the  pulley,  it  is  necessary  to  make  the  weight  W2  of 
such  a  magnitude  that  it  will  overcome  not  only  the  weight  W,. 
but  also  the  friction  between  the  strap  and  the  pulley.  The  strap 
tension  Tr  is.  of  course,  equal  to  ~\V. .  and  T0  to  "W,.  The  equation 
showinn-  the  balance  of  forces  for  the  condition  when  motion  is 
about  to  occur,  is: 

Tn  -  To  =  F  =  P  (  driving  force).  (5) 

If  the  pulley  be  free  to  turn  on  its  axis,  instead  cf  beingfixed 

as  in  Fig.  17,  the  strap  by  its 
friction  on  the  pulley  will  turn 
the  pulley,  and  the  force  of 
friction  F  becomes  the  driving 
force  for  the  pulley  as  noted 
in  equation  5  above. 

In  Fig.  18,  let  us  sup- 
pose that  "W  is  a  weight  repre- 
senting the  resistance  to  be 
overcome.  The  tensions  Tn 
and  T0,  equal  at  first  owing  to 
stretching  the  belt  tightly 
over  the  pulleys  at  rest,  change 
when  an  attempt  is  made  to 
raise  the  weight  by  turning 
the»larger  pulley;  and  just  as 
the  weight  leaves  the  floor,  the 
equality  of  moments  about 
the  axis  of  the  driven  pulley 
gives  the  following  equation: 

(TU  '-  T0)  r  =  F  Xr  =  Pxr  =  W  X  r,.          (6) 

This  equality  of  moments  remains  as  long  as  the  motion  of 
the  weight  is  uniform,  and  represents  closely  the  conditions  under 
which  belt  pulleys  work. 

Although  we  know  from  the  above  what  the  difference  of  the 
belt  tensions  is,  and  what  this  difference  will  do  when  applied  to 


Fig.  17. 


MACHINE  DESIGN 


79 


the  surface  of  a  given  pulley,  we  do  not  yet  know  what  either 
Tn  or  T0  actually  is;  and  until  we  do  know,  we  cannot  correctly 
proportion  the  belt.  Hence  we  must  find  another  relation  between 
Tn  and  T0  which  we  can  combine  with  equations  5  and  6.  This 
relation  is  deduced  by  a  process  of  higher  mathematics,  which  re- 
sults as  follows: 

T 

Common  logarithm  rp2-  =  2.729  p  (1  -  s)n.      (7) 

Treating  equations  5  and  7  as  simultaneous,  values  of  both 
Tn  and  T0  can  be  found  by  the  regular  algebraic  solution.  As  Tn 
is  the  larger,  the  actual  area  of  belt  to  provide  the  necessary  strength 
must  be  made  to  depend  upon  it. 

The  factors  in  equation  7  depends  upon  the  centrifugal  force 


Fig.  18. 

developed  by  the  weight  of  the  belt  passing  around  the  pulley.     Its 
value,  found  from  mechanics,  is: 

w  X  V2 
=  9,660  X  f" 

Having  found  the  maximum  pull  on  the  belt,  it  now  remains 
to  write  the  equation: 

External  force  =  Internal  resistance; 
or,  Tn  =  I  X  h  X  t.  (8) 

Usually  the  most  convenient  way  to  handle  this  equation  is 
to  assume  k  and  t,  and  then  solve  for  b. 


80  MACHINE  DESIGN 


Summing  up  the  theoretical  treatment  of  belt  design,  we 
simply  combine  equations  5,  0,  7.  and  S,  and  solve  for  the  quantity 
desired.  Discussion  of  the  constants  involved  in  these  equations, 
and  of  the  practical  factors  controlling  them,  is  given  in  the  fol- 
lowing : 

PRACTICAL  MODIFICATION.  The  force  of  friction  F.  which 
is  the  same  as  driving  force  P.  depends  on: 

Coefficient  of  friction  (/zi  between  belt  and  pulley; 

Tightness  of  the  belt; 

Centrifugal  force  of  the  belt; 

Angle  of  contact  of  belt  with  pulley. 

The  coefficient  of  friction  (^),  according  to  experiments  and 
observed  operation  of  belts  transmitting  power,  varies  from  .15  to 
.51)  for  leather  on  cast  iron.  An  average  value  consistent  with  a 
reasonable  amount  of  slip,  the  belt  being  in  good  running  order, 
is  .30.  If  the  belt  is  oily,  or  likely  to  become  so  in  use,  a  lower 
value  should  be  taken. 

The  tighter  the  belt  is  drawn  up,  the  greater  is  the  pressure 
against  the  pulley,  and  hence  the  greater  is  the  force  of  friction. 
But  if  we  pull  the  belt  up  too  tightly,  when  we  begin  to  drive, 
Tn  becomes  too  great,  and  the  belt  breaks  or  is  under  such  stress 
that  k  wears  out  quickly.  Moreover,  the  great  side  pressure  on 
the  bearings  carrying  the  shaft  produces  excessive  friction,  and  the 
drive  is  inefficient.  This  is  why  a  narrow  belt  driven  at  hio-h 

*/  O 

speed  is  more  efficient  than  a  wide  belt  at  slow  speed,  for  we  can- 
not pull  up  the  former  as  tightly  as  the  latter  without  overstraining 
it.  and  yet  it  is  possible  to  get  the  required  power  out  of  the  nar- 
row belt  by  running  it  at  high  speed. 

The  centrifugal  force  is  of  small  importance  for  low  speeds, 
say  of  3.000  feet  per  minute  and  less;  and  it  therefore  may  usu- 
ally be  neglected.  The  factor  z  then  becomes  zero  in  the  expres- 
sion 1-2  in  equation  7,  and  the  second  member  of  the  equation 
stands  simply  2.729  X  /u,  X  />. 

The  angle  of  contact  of  belt  with  pulley  is  important,  as  a 
large  value  gives  a  great  difference  between  Tu  and  T0;  and  it  is 
desirable  to  make  this  difference  as  great  as  possible,  because  there- 
by the  driving  force  is  increased.  The  loose  side  of  a  horizontal 
belt  should  always  be  above,  as  then  the  natural  sag  of  the  loose 


94 


MACHINE  DESIGN  81 

side  due  to  its  slackness  tends  to  increase  the  angle  of  contact  with 
the  pulley,  -while  the  tightening  up  of  the  lower  side  acts  against 
its  sag  to  make  the  loss  of  wrap  as  little  as  possible.  Vertical  belts 
which  have  the  driving  pulley  uppermost,  utilize  the  weight  of  the 
belt  to  increase  the  pressure  against  the  surface  of  the  pulley,  slightly 
increasing  its  capacity  for  driving.  The  angle  of  contact  may 
be  artificially  increased  by  a  tightening  pulley  which  presses  the 
belt  -further  around  the  pulley  than  it  would  naturally  lie.  It 
adds  however,  the  friction  of  its  own  bearing,  and  impairs  the  effi- 
ciency of  the  drive.  For  ordinary  horizontal  belts,  the  angle  of 
contact  is  but  little  more  than  180°,  and  the  value  of  n  in  equation 
7  may  be  safely  assumed  at  ^  unless  the  pulleys  are  of  relatively 
great  difference  of  diameter  and  very  close  together. 

Strength  of  Leather  Belting.  The  breaking  tensile  strength 
of  leather  belting  varies  from  3,000  to  5,000  pounds  per  square 
inch.  Joints  are  made  by  lacing,  by  metal  fasteners,  or  by  cement- 
ing. The  strength  of  a  laced  joint  may  be  about  T7T,  of  a  metal- 
fastened  joint,  about  |,  and  of  a  cemented  joint,  about  equal  to 
the  full  strength  of  the  belt  cross-sectional  area.  The  proper 
working  strength  of  belting  depends  on  the  use  to  which  the  belt 
is  put.  A  continuously  running  belt  should  have  a  low  tension 
in  order  to  have  long  life  and  a  minimum  loss  of  time  for  repairs. 
For  double  leather  belting  it  has  been  shown  that  a  working  ten- 
sion of  240  pounds  per  square  inch  of  sectional  area  gives  an  an- 
nual cost  —  for  repairs,  maintenance,  and  renewals — of  14  per 
cent  of  first  cost.  At  400  pounds  working  tension,  the  annual  ex- 
pense becomes  37  per  cent  of  first  cost.  These  results  apply  to 
belts  running  continuously;  larger  values  may  be  used  where  the 
full  load  comes  on  but  a  short  time,  as  in  the  case  of  dynamos. 

Good  average  values  for  working  tensions  of  leather  belts  are: 

Cemented  joints,  400  pounds  per  square  inch. 
Laced  joints,         300     "  "        "          " 

Metal  joints,          250     "  "        "          " 

Horse=Power  Transmitted  by  Belting.  If  P  is  the  driving 
force  in  pounds  at  the  rim  of  the  pulley,  and  V  is  the  velocity  of 
the  belt  in  feet  per  minute,  the  theoretical  horse-power  transmitted 
is  evidently  : 


05 


82  MACHINE  DESIGN 


It  is  evident  from  the  above  that  the  horse-power  of  a  belt  .de- 
pends upon  two  things,  the  driving  force  Pand  the  velocity  V.  If 
either  of  these  factors  is  increased,  the  horse-power  is  increased. 
Increasing  P  means  a  ticrkt  belt.  Hence  a  tifht  belt  and  hio-h 

O  &  ^5  O 

speed  together  give  maximum  horse-power.  But  a  tight  belt 
means  more  side  strain  on  shaft  and  journal.  Therefore,  from  the 
standpoint  of  efficiency,  -use  a  narrow  belt  under  low  tension  at  as 
hiyh  a  speed  as  possible. 

Empirical  rules  for  horse-power  of  belting,  if  used  with  judg- 
ment, give  safe  results  when  applied  to  very  general  cases.  A 
common  rule  used  by  American  engineers  is: 


For  a  double  belt,  assuming  double  strength,  this  becomes: 


With  large  pulleys  and  moderate  velocities,  this  may  hold 
good.  AVith  small  pulleys  and  high  velocities,  however,  the  un- 
certain stresses  induced  by  the  bending  of  the  libers  of  the  belt 
around  the  pulley,  and  the  relatively  great  loss  due  to  centrifugal 
force,  modify  this  relation1  and  a  safer  value  for  a  double  belt  of 
the  ordinary  kind  is: 


or.  still  safer.  II.  P.  =  -jffi-  (13) 

If  we  compare  the  theoretical  value  of  equation  9  with  the 
empirical  value  of  equation  10  by  putting  them  equal  -to  each 
other,  thus: 

11    P    -  P  X  Y='J  XV 
83.000  ~~  1,000  ' 

and  solve  for  P,  we  get  : 


D6 


MACHINE  DESIGN  83 


P  =  33£. 


(14) 


This  develops  ^the  fact  that  the  empirical  rule  of  equation  ]0  as- 
sumes a  driving  force  of  33  pounds  per  inch  of  width  of  single 
belt. 

Another  way  of  expressing  equation  10  is:  A  single  belt 
will  transmit  one  horse-power  for  every  inch  of  width  at  a  belt 
speed  of  1,000  feet  per  minute. 

Speed  of  Belting.  The  most  economical  speed  is  somewhere 
between  4,000  and  5,000  feet  per  minute.  Above  these  values 
the  life  of  the  belt  is  shortened;  also  "flapping,"  "chasing,"  and 
centrifugal  force  cause  considerable  loss  of  power.  The  limit  of 
speed  with  cast-iron  pulleys  is  fixed  at  the  safe  limit  for  bursting 
of  the  rim,  which  may  be  taken  at  one  mile  per  minute. 

Material  of  Belting.  Oak-tanned  leather,  made  from  the 
part  of  the  hide  which  covers  the  back  of  the  ox,  gives  the  best  re- 
sults for  leather  belting.  The  thickness  of  the  leather  varies 
from  .18  to  .25  inch.  It  weighs  from  .03  to  .04  pound  per  cubic 
inch.  The  average  thickness  of  double  leather  belts  may  be  taken 
as  .33  inch,  although  a  variation  in  thickness  from  \  inch  to  T7T 
inch  is  not  uncommon.  Double  leather  belts  may  be  ordered 
light,  medium,  or  heavy. 

In  a  single- thickness  belt  the  grain  or  hair  side  should  be 
next  to  the  pulley,  for  the  flesh  side  is  the  stronger  and  is  there- 
fore better  able  to  resist  the  tensile  stress  due  to  bending  set  up 
where  the  belt  makes  and  leaves  contact  with  the  pulley  face. 
Double  leather  belts  are  made  by  cementing  the  flesh  sides  of 
two  thicknesses  of  belt  together,  leaving  the  grain  side  exposed 
to  surface  wear. 

Raw  hide  and  semi-raw  hide  belts  have  a  slightly  higher  co- 
efficient of  friction  than  ordinary  tanned  belts.  They  are  useful  in 
damp  places.  The  strength  of  these  belts  is  about  one  and  one- 
half  times  that  of  tanned  leather. 

Cotton,  cotton -leather,  rubber,  and  leather  link  belting  are 
some  of  the  forms  on  the  market,  each  of  which  is  especially 
adapted  to  certain  uses.  For  their  weights  and  their  tensile  and 
working  strengths  consult  the  manufacturers'  catalogues. 

A  prominent  manufacturer's  practice  in  regard  to  the  sizes  of 


97 


MACHINE  DESIGN 


leather  belting  will  he  found  useful  for  comparison,  and  is  indicated 
in  the  table  on  page  12. 

Initial  Tension  in  Belt.  On  the  assumption  that  the  sum  of 
the  tensions  is  unchanged,  whether  the  belt  be  at  rest  or  driving, 
we  should  have  the  following  relation  : 


whence. 


T  = 


1V4-T 


(IS) 


This  is  not  strictly  true,  however,  as  is  stated  in  the  i%  Analysis' 
of  '-  Belts. ''  It  has  been  found  that  in  a  horizontal  belt  working  at 
about  400  Ibs.  tension  per  square  inch  on  the  tight  side,  and  hav- 
ing 2  per  cent  slip  on  cast-iron  pulleys  ( i.  e.,  the  surface  of  the 

Sizes  of  Leather  Belting. 


WIDTH. 

THICKNESS. 

Single. 

Double. 

1  inch. 

yV  inch. 

f'u  inch. 

2    " 

T5,       " 

3    " 

7         u 
¥2" 

3         u 

'    "ff 

4     " 

*V   " 

1        "' 

5     " 

sV     " 

f        " 

6    " 

sV     " 

f        " 

10    " 

5         u 
T6" 

3.        <; 

12     " 

f        " 

14     " 

M       " 

20    "             

TV      " 

driven  pulley  moving  2  per  cent  slower  than  that  of  the  driver), 
the  increase  of  the  sum  of  the  tensions  when  in  motion  over  the 
sum  of  the  tensions  at  rest,  may  be  taken  at  about  ^  the  value  of 
the  tensions  at  rest.  Expressing  this  in  the  form  of  an  equation 

Tn  +  T.^^T)^8-^. 


—  _     fT    _|_  T  \ 
-cT    kAn    '     Aoj- 


(16) 


MACHINE  DESIGN  85 

The  value  of  T  thus  found  would  be  the  pounds  initial  tension  to 
which  the  belt  should  be  pulled  up  when  being  laced,  in  order  to 
produce  Tn  and  T0  when  driving. 

This  value  is  not  of  very  great  practical  importance,  as  the 
proper  tightness  of  belt  is  usually  secured  by  trial,  by  tightening 
pulleys,  by  pulley  adjustment  (as  in  motor  drives),  or  by  shorten- 
ing the  belt  from  time  to  time  as  needed.  It  is  worth  noting, 
however,  that  for  the  most  economical  life  of  the  belt  it  would  be 
very  desirable  in  every  case  to  weigh  the  tension  by  a  spring  bal- 
ance when  giving  the  belt  its  initial  tension.  This,  however,  is 
not  always  easy  or  even  feasible;  hence  it  is  a  refinement  with 
which  good  practice~usually  dispenses,  except  in  the  case  of  large 
and  heavy  belts. 

PROBLEMS  ON   BELTS. 

1.  Determine  the  belt  tensions  in  a  laced  belt  transmitting  50 
horse-power  at  a  velocity  of  3,500  feet  per  minute.     Suppose  that 
the  arc  of  contact  is  180°;  weight  of  belt  =  .035  pound  per  cub. 
In.;  and  coefficient  of  friction  25  per  cent. 

2.  What  is  the  width  of  above  belt  if  it  is  T3¥  inch  in  thick- 
ness ? 

3.  What  initial  tension  must  be  placed  on  above  belt  ? 

4.  The  main  drive  pulley  of  a  120-horse-power  water  wheel 
is  6  feet  in  diameter.     A  cemented  leather  belt  is  to  connect  the 
main  pulley  to  a  3-foot  pulley  on  the  line  shafting  in  a  mill.    The 
horizontal  distance  between  centers  of  shafting  is  24  feet;  coeffi- 
cient of  friction,  30  per  cent;  revolutions  per  minute  of  line  shaft- 
ing, 180.     DesJgn  the  belt  for  this  drive. 

5.  An  8-.inch  double  belt  ^  inch  thick  connects  2  pulleys  of 
30-inch  and  20-inch  diameter  respectively.     The  horizontal  dis- 
tance between  the  centers  is  12.5  feet.     The  coefficient  of  friction 
is  0.3,  and  the  weight  of  belt  per  cubic  inch  is  0.035  pound. 
Working  tension,  300  pounds  per  square  inch.     Speed  of  belt 
5,000  feet  per  minute.     Lower  face  of  30-inch  pulley  is  the  driv- 
ing face.     Required  the  H.  P.  which  may  be  transmitted  (theo- 
retically). 

6.  Compare  the  theoretical  horse-power  in  problem  5  with 
that  obtained  by  the  use  of  empirical  formula. 


09 


86  MACHINE  DESIGN 


PULLEYS. 

NOTATION— The  following  notation  is  used  throughout  the  chapter  on  Pulleys: 

A  =  Area  of  rim  (sq.  in.).  I    =  Length  of  hub  (inches). 

a  —     "     "  arm  ( '•      •'  ).  N  =  Number  of  arms. 

b   =Center  of  pulley  to  center  of  belt  n  =        "         "  rim  bolts,  each  side. 

(inches;  practically  equal  to  R).  P  ^Driving  force  of  belt  (Ibs.). 

C'i  =  Total  centrifugal  force  of  rim  (Ibs.).  Pi  =  Forcc    at    circumference   of     shaft 
c    =  Distance  from  neutral  axis  to  outer  (Ibs.). 

fiber  (inches).  Pi=  Force  at  circumference  of  hub  (Ibs.). 

D  =  Diameter  of  pulley  (inches).  p   —  Stress  in  rim  due  to  centrifugal  force 
DI-         "            "hub       (      "      ).  (Ibs.  per  sq.  in.). 

(/!  =        '•  "bolt  at   root  of  thread  R  =Raclius  of  pulley  (inches). 

(inche.-).  S   -Fiber  stress  (Ibs.  per  sq.  in.). 

(/    --Diameter  of  bolt  holes  (inches).  s  -Fiber  stress  in  flange  (Ibs.  persq.  in.). 

H    =  Acceleration     due    to     gravity    (ft.  T  =  Thickness  of  web  (inches). 

per  sec.).  t     —          "  ''   rim   (      "      ). 

/i    =  Width  of  arm  at  any  section  (inche.-).  /2    -        "  "     "  bolt  flange  (inches). 

I    =  Moment  of  inertia-  T  u  =  Tension  of  belt  on  tight  side  (Ibs.). 

L  =  Length  of  arm,  center  of  belt  to  hub  T0=        "        "     "      "loose    "     (  "  ). 

(inches).  v    =  Velocity  of  rim  (ft.  per  sec.). 

Li=Length  of  rim  flange  of  split  pulley  »/•  =Weightof  material  (Ibs.  per  cub. in.). 

(inches). 

ANALYSIS.     If  a  flexible  band  be  wrapped  completely  about 

a  pulley,  and  a  heavy  stress  be  put  upon  each  end  of  the  band,  the 
rim  of  the  pulley  will  tend  to  collapse  just  like  a  boiler  tube  with 
steam  pressure  on  the  outside  of  it.  A  compressive  stress  is  in- 
duced which  is  very  nearly  evenly  distributed  over  the  cross-sec- 
tion of  the  rim,  except  at  points  where  the  arms  are  connected 
thereto.  At  these  points  the  arms,  acting  like  rigid  posts,  take 
this  cornpressive  stre'ss.  Now,  a  pulley  never  has  a  belt  wrapped 
completely  round  it,  the  fraction  of  the  circumference  embraced  by 
the  belt  being  usually  about  A,  and  seldom,  even  with  a  tightener 
pulley,  reaching  |.  Assuming  the  wrap  to  be  4-  the  circumference, 
and  that  all  the  side  pull  of  the  belt  comes  on  the  rim.  none  being 
transmitted  through  the  arms  to  the  hub,  we  then  have  one-half  of 
the  rim  pressed  hard  against  the  other  half  by  a  force  equal  to  the 
resultant  of  the  belt  tensions,  which,  in  this  case,  would  be  the 
sum  of  them.  Dividing  the  pulley  by  a  plane  through  its  center 
and  perpendicular  to  the  belt,  the  cross-section  of  the  rim  cut  by 
this  plane  has  to  take  this  compressive  stress- 

This  analysis  is  satisfactory  from  an  ideal  standpoint  only,  for 
the  intensity  of  stress  due  to  the  direct  pull  of  the  belt,  with  the 
usual  practical  proportions  of  rim,  would  be  very  small.  More- 
over, the  element  of  speed  has  not  been  considered. 

When  the  pulley  is   under  speed,  a   set  of  conditions  which 


100 


MACHINE  DESIGN  87 

complicates  matters  is  introduced.  The  centrifugal  force  due  to 
the  weight  of  the  rim  and  arms  is  no  longer  negligible,  but  has 
an  important  influence  upon  the  design  and  material  used.  This 
centrifugal  force  acts  against  the  effect  of  the  belt  wrap,  tending 
to  reduce  the  compressive  stress,  or,  overcoming  the  latter  entirely, 
sets  up  a  tensional  stress  both  in  the  rim  and  in  the  arms.  It  also 
tends  to  distort  the  rim  from  a  true  circle  by  bowing  out  the  rim 
between  the  arms,  thus  producing  a  bending  moment  in  the  rim, 
maximum  at  the  points  where  the  rim  joins  each  arm. 

It  can  readily  be  imagined  that  the  analysis  in  detail  of  these 
various  stresses  in  the  rim  acting  in  conjunction  with  each  other 
is  quite  complicated  —  far  too  much  so  in  fact,  to  be  introduced 
here.  As  in  most  cases  of  such  design,  however,  one  controll- 
ing influence  can  be  separated  out  from  the  others,  and  the  de- 
sign based  thereon  with  sufficient  margin  of  strength  to  satisfy 
the  more  obscure  conditions.  This  is  rational  treatment,  and  the 
"  theory  "  will  be  studied  accordingly. 

The  rim,  being  fastened  to  the  ends  of  the  arms,  tends,  when 
driving,  to  be  sheared  off,  the  resisting  area  being  the  areas  of  the 
cross-sections  of  the  arms  at  their  point  of  joining  the  rim.  The 
force  that  produces  this  shearing  tendency  is  the  driving  force  of 
the  belt,  or  the  difference  between  the  tensions  of  the  tight  and 
loose  sides. 

Again,  at  the  point  of  connection  of  the  arms  to  th«  hub,  s 
shearing  action  takes  place,  so  that,  if  this  shearing  tendency  were 
carried  to  rupture,  the  hub  would  literally  be  torn  out  of  the  arms. 
Now,  viewing  the  arms  as  beams  loaded  at  the  end  with  the  driv- 
ing force  of  the  belt,  and  fixed  at  the  hub,  a  heavy  bending  stress 
is  set  up,  which  is  maximum  at  the  point  of  connection  to  the 
hub.  If  the  rim  were  stiff  enough  to  distribute  this  driving  force 
equally  between  the  arms,  each  arm  would  take  its  proportional 
share  of  the  load.  The  rim,  however,  is  quite  thin  and  flexible; 
and  it  is  not  safe  to  assume  this  perfect  distribution.  It  is  usual 
to  consider  that  one-half  the  whole  number  of  arms  take  the  full 
driving  force. 

THEORY— Pulley  Rim.  Evidently  it  is  practically  impossible 
to  make  so  thin  a  rim  that  it  will  collapse  under  the  pull  of  a  belt. 
As  far  as  the  theory  of  the  rim  is  concerned,  its  proportion  prob- 


101 


MACHINE  DESIGN 


ably  depends  more   upon  the  calculation  for  centrifugal  force  than 
upon  anything  else. 

In  order  to  separate-  this  action  from  that  of  any  other  forces, 
let  us  suppose  that  the  rim  is  entirely  free  from  the  arms  and  hub. 
and  is  rotating  about  its  center.  Every  particle,  by  centrifugal 
force,  tends  to  liy  radially  outward  from  the  center.  This  condi- 
tion is  represented  in  Fig.  1'-).  The  tendency  with  which  one-half 
of  the  rim  tends  to  tiy  apart  from  the  other  is  indicated  by  the 
force  C,;  and  the  relation  between  C,  and  the  small  radial  force  c 
for  each  unit-length  of  rim  can  readily  be  found  from  the  prin- 
ciples of  mechanics.  The  case  is  exactly,  like  that  of  a  boiler  or  a 
thin  pipe  subjected  to  uniform  internal  pressure,  which,  if  carried 
to  rupture,  would  split  the  rim  along  a  longitudinal  seam. 


Fig.  19. 

The  tensile  stress  thus  induced  per  square  inch  can  be  found 
by  simple  mechanics  to  be: 


or,  since  ?/•  --  0.2»>  pound,  and  y  =-  3'2.2  feet  per  second. 

Jt  =  0.01)7  -e*     (    say-^j)  5  (l8) 

and.  ify/  be  taken  equal  to  1,000  pounds  per  square  inch,  which  is 
as  high  as  it  is  safe  to  work  cast  iron  in  this  place, 

v  =  100  feet  per  second.  (i9) 

This  shows  the  curious   fact  that  the  intensity  of  stress  in  the  rim 


102 


MACHINE  DESIGN 


89 


is  directly  proportional  to  the  square  of  the  linear  velocity,  and 
wholly  independent  of  the  area  of  cross -section.  It  is  also  to  be 
noted  that  100  feet  per  second  is  about  the  limit  of  speed  for  cast- 
iron  pulleys  to  be  safe  against  bursting. 

If  we  wish  to  consider  theoretically  the  rim  together  with  the 
arms  as  actually  connected  to  it,  we  get  a  much  more  complicated 
relation.  This  condition  is  shown  in  Fig.  20,  where  the  rim,  ex- 
panding more  than  the  arms,  bulges  out  between  them.  This 
makes  the  rim  act  something  like  a  continuous  beam  uniformly 
loaded;  but  even  then  the  resulting  stress  is  not  clearly  defined  on 
account  of  the  variable  stretch  in  the  arms.  Investigation  on  this 
basis  is  not  needed  further  than  to  note  that  it  is  theoretically 
better,  in  the  case  of  a  split  pulley,  to  make  the  joint  close  to  the 
arms,  rather  than  in  the  middle  of  a  span. 

Pulley  Arms.  The  centrifugal  force  developed  by  the  rim 
and  arms  tends  to  piill  the  arms  from  the  hub.  On  the  belt  side, 
this  is  balanced  to  some  extent  by  the  belt  wrap,  which  tends  to 
compress  the  arm  and  relieve  the  tension.  On  the  side  away 
from  the  belt,  the  centrifugal  action  has 
full  play,  but  the  arm  is  usually  of  such 
cross-section  that  the  intensity  of  this  stress 
is  very  low.  It  may  safely  be  neglected. 

The  rim  being  very  thin  in  most  cases, 
its  distributing  effect  cannot  be  depended 
on,  hence  the  driving  force  of  the  belt  may 
be  taken  entirely  by  the  arms  immediately 
under  the  portion  of  the  belt  in  contact  with 
the  pulley  face.  For  a  wrap  of  180°  this 


Fig.  21. 


means  that  only  one-half  of  the  pulley  arms  can  be  considered  as 
effective  in  transmitting  the  turning  effort  to  the  hub.  Each  of 
these  arms  is  a  lever  fixed  at  one  end  to  the  hub  and  loaded  at  the 
pther.  A  lever  of  this  description  is  called  a  "  cantilever  "  beam, 
its  maximum  moment  existing  at  its  fixed  end.  The  load  that  each 

p 
of  these  beams  may  be  subjected  to  is-^-,   and  therefore  the  maxi- 


imnrn  external  moment  at  the  Irob  is 


2PL 


From   mechanics  we 


103 


90  MACHINE  DESIGN 


know  that  the  internal  moment  of  resistance  of  any  beam  section 
is  —  ,  and    that   equilibrium   of   the    beam    can    be   satisfied  only 

when  the  external  moment  is  equal  to  the  internal  moment  of  re- 
sistance of  the  beam  section.     Equating  these  two,  we  have: 

2PL        SI 


The  arms  of  a  pulley  are  usually  of  the  elliptical  or  segmental 
cross-section,  and    may  be  of   the  proportions    shown    in   Fig.  21. 

For  either  of  these  sections  the  fraction  —  is  approximately  equal 

to  0.0393/>3.  For  convenience  (the  error  caused  being  on  the  safe 
side).  L  may  be  taken  as  equal  to  the  full  radius  of  the  pulley  R, 
whence 

•>PR        9,T     __  T    ,P 

4^         (1"N>)K  =  0.0393S/,',  (21) 

in  which  S  may  be  from  2.000  to  2,250  for  cast  iron 

Taking  moments  about   the  center  of  the  pulley,  and   solving 
for  P,.  the  force  acting  at  the  circumference  of  the  hub,  we  have  : 

2PE      P0D, 


P2  =      ~  (22) 


The  area  of  an  elliptical  section  is   IT  times  the  product  of  the 
half  axes.     AVith  the  proportions  of  Fig.  21.  this  becomes: 

<>  =  77  X  0.27,  X  0.5/<  =  ~  (23) 

Equating  the  external  force  to  the  internal  shearing  resistance,  we 
have  : 

4PR  _  7r/rSs 
ND,  -     TIT 

Sa  =  =  4^^ 


104 


MACHINE  DESIGN 


91 


in  which  the  shearing  stress  Ss  may  ran  from  1,500  to  1,800  for 
cast  iron. 

Although  -both  bending  and  shearing  stresses  as  calculated 
above  exist  at  the  base  of  the  arms,  the  bending  is,  in  practically 
every  case,  the  controlling  factor  in  the  design  of  the  arms.  An 
arm-section  large  enough  to  resist  bending  would  have  a  very  low 
intensity  of  shear. 

If  the  number  of  arms  be  increased  indefinitely,  we  come  to 
a  continuous  arm  or  web,  in  which  the  bending  action  is  elimi- 
nated. It  may  still  shear  off  at  the  hub,  where  the  area  of  metal 
is  the  least,  at  minimum  circumference.  In  this  case  the  area 
under  shearing  stress  is  ^DjT;  and  the 'force  at  the  circumference 
of  the  hub,  is 

PR     2PR 


D, 


Equating  external  force  to  in- 
ternal shearing  resistance,  we 
have  : 


(25) 


or,       ,= 


Fig.  22. 


Pulley  Hub.     As  in  the 

case  of  the  arms,  centrifugal 
force  does  not  play  much  part  in  the  design  of  the  hub  of  a  pulley. 
The  hub  is  designed  principally  to  carry  the  key,  and  through  it 
transmit  the  turning  moment  to  the  shaft.  Considered  thus,  the 
hub  may  tear  along  the  line  of  the  key  or  crush  in  front  of  the  key. 
For  example,  in  Fig.  22,  if  the  connection  with  the  lower 
arms  be  neglected,  and  the  upper  arms  be  held  fast  while  a  turning 
force  P,,  at  the  surface  of  the  shaft,  is  transmitted  to  the  hub 
through  the  key,  then  the  metal  of  the  hub  directly  in  front  of  the 
key  is  under  crushing  stress;  and  the  metal  along  the  line  eb,  from 
the  corner  to  the  outside,  is  under  tensile  stress.  This  condition  is 
the  worst  that  could  possibly  happen,  because  the  bracing  effect  of 
the  lower  arms  has  been  neglected,  and  the  key  is  located  between 
the  arms. 


105 


02  MACHINE  DESIGN 


Takino-  moments  about  the  center  of  the  shaft,  the  value  of  the 
force  at  the  shaft  circumference,  or  the  '-key  pull,"  is: 

p.=™:  (26) 

P        /' 

Xow-n          —  .  k  being  the  distance  from    the   center   of  shaft    to 
P,          i- 

center  of  cb.  and  the  area  of  metal  which  is  subjected  to  the  tearing 
action  P.^  is  /  /;  <:b.  Equating  the  external  force  to  the  internal 
resistance,  and  assuming  that  the  stress  is  equally  distributed  over 
the  area  /  '/.  cb,  we  have: 

3        /•      !         /,'    ^      i'  ' 


The  intensity  of  crushing  on  the  metal  in  front  of  the  key,  due 
to  force  P,.  depends  upon  the  thickness  of  the  key,  and  is  properly 
discussed  later  under  "Keys." 

PRACTICAL  MODIFICATION— Pulley  Rim.  The  theoretical 
calculation  for  the  thickness  of  the  rim  may  give  a  thickness  that 
could  not  be  cast  in  the  foundry,  and  the  section  in  that  case  will 
have  to  be  increased.  As  light  a  section  as  can  be  readily  cast  will 
usually  be  found  abundantly  strong  for  the  forces  it  has  to  resist. 
A  minimum  thickness  at  the  edge  of  the  rim  is  about  T3(}  inch; 
and  as  the  pulleys  increase  in  size,  the  rim  also  must  be  made 
thicker;  otherwise  the  rim  will  cool  so  much  more  quickly  than 
the  arms,  that  the  latter,  on  cooling,  will  develop  shrinkage  cracks 
at  the  point  of  junction. 

For  a  velocity  of  0.000  feet  per  minute,  we  find  from  equation 
1"5  that  the  tension  in  pounds  per  square  inch,  in  the  rim,  due  to 
centrifugal  force,  is  970.  Though  this  in  itself  is  a  low  value,  yet 
the  uncertain  nature  of  cast  iron,  its  condition  of  internal  stress, 
due  to  casting,  and  the  likely  existence  of  hidden  flaws  and  pockets, 
have  established  the  usage  of  this  figure  as  the  highest  safe  limit 
for  the  peripheral  speed  of  cast-iron  pulleys.  It  is  easily  remem- 
bered that  riixt-iroii  }>till<:ij*  ar<-  znf<>  for  a  l>n<*'ir  velocity  of  about 
out  mi  If  in:  r  in 'm  iitc. 


106 


MACHINE  DESIGN 


To  prevent  the  belt  from  running  off  the  pulley,  a  "crown" 
or  rounding  surface  is  given  the  rim.  A  tapered  face,  which  is 
more  easily  produced  in  the  ordinary  shop,  may  be  used  instead. 
This  taper  should  be  as  little  as  possible,  consistent  with  the  belt 
staying  on  the  pulley;  ^  inch  per  foot  each  way  from  the  center 
is  not  too  much  for  faces  4  inches  wide  and  less;  while  above  this 
width  ^  inch  per  foot  is  enough.  As  little  as  J  inch  total  crown 
has  been  found  to  be  sufficient  on  a  24-inch  face,  but  this  is 
probably  too  little  for  general  service. 

Instead  of  being  "crowned,"  the  pulley  may  be  flanged  at  the 
edges;  but  flanged  pulley  rims  chafe  and  wear  the  edge  of  the  belt. 

The  inside  of  the  rim  of  a  cast-iron  pulley  should  have  a  taper 
of  4  inch  per  foot  to  permit  easy  withdrawal  from  the  foundry 


Fig.  23. 

mould.  This  is  known  as  "draft."  If  the  pattern  be  of  metal,  or 
if  the  pulley  be  machine-moulded,  the  greater  truth  of  the  casting 
does  not  require  that  the  inside  of  the  rim  be  turned,  as  the  pulley, 
at  low  speeds,  will  be  in  sufficiently  good  balance  to  run  smoothly.- 
For  roughly  moulded  pulleys,  and  for  use  at  high  speeds,  however, 
it  is  necessary  that  the  rim  be  turned  on  the  inside  to  give  the 
pulley  a  running  balance. 

Fig.  23  shows  a  plain  rim  a  also  one  stiffened  by  a  rib  b. 
Where  heavy  arms  are  used  this  rib  is  essential  so  that  there  will 
not  be  too  sudden  change  of  section  at  the  junction  of  rim  and  arm. 
and  consequent  cracks  or  spongy  metal. 

Pulley  Arms.  The  arms  should  be  well  filletted  at  both  "rim 
and  hub,  to  render  the  flow  of  metal  free  and  uniform  in  the  mould. 
The  general  proportions  of  arms  and  connections  to  both  hub  and 
rim  may  perhaps  be  best  developed  by  trial  to  scale  on  the  draw- 
ing board.  The  base  of  the  arm  being  determined,  it  may  gradu- 


107 


94  MACHINE  DESIGN 

ally  taper  to  the  rim,  where  it  takes  about  the  relation  of  §  to  | 
the  dimensions  chosen  at  the  hub.  The  taper  may  be  modified 
until  it  looks  right,  and  then  the  sizes  checked  for  strength. 

Six  arms  are  used  in  the  great  majority  of  pulleys.  This 
number  not  only  looks  well,  but  is  adapted  to  the  standard  three- 
jawed  chucks  and  common  clamping  devices  found  in  most  shops. 
Elliptical  arms  look  better  than  the  segmental  style.  The  flat, 
rectangular  arm  gives  a  very  clumsy  and  heavy  appearance,  and  is 
seldom  found  except  on  the  very  cheapest  work. 

A  double  set  of  arms  may  be  used  on  an  excessively  wide 
face,  but  it  complicates  the  casting  to  some  extent. 

Although  a  web  pulley  may  be  calculated  for  shear  at  the 
hub.  yet  it  will  usually  be  found  that  with  a  thickness  of  web  in- 
termediate between  the  thickness  of  the  rim  and  that  of  the  hub. 
which  will  satisfy  the  casting  requirements,  the  requirements  as  to 
strength  will  by  fully  met. 

Pulley  Hub.  The  hub  should  have  a  taper  of  i  inch  per  foot 
draft,  similar  to  that  of  the  inside  of  the  rim.  The  length  of  the 
hub  is  arbitrary,  but  should  be  ample  to  prevent  rocking  on  the 
shaft.  A  common  rule  is  to  make  it  about  |  the  face  width  of 
the  pulley. 

The  diameter  of  the  hub,  aside  from  the  theoretical  consider, 
ation  given  above,  must  be  sufficient  to  take  the  wedging  action  of  a 
taper  key  without  splitting.  This  relation  cannot  well  be  calcu- 
lated. Probably  the  best  rule  that  exists  is  the  familiar  one  that 
the  hub  should  be  twice  the  diameter  of  the  shaft.  This  rule, 
however,  cannot  be  literally  adhered  to.  as  it  gives  too  small  hubs 

for  small  shafts  and  too  laro-e  ones  for  laro-e  shafts.      It  is  always 

G  •/ 

well  to  locate  the  key,  if  possible,  underneath  an  arm  instead  of 
between  the  arms,  thus  gaining  the  additional  strength  due  to  the 
backing  of  the  arm. 

SPLIT  PULLEYS. 

ANALYSIS  and  THEORY.  The  split  pulley  is  made  in 
halves  and  provided  with  bolts  through  flanges  arid  bosses  on  the 
hub  for  holding  the  two  halves  together.  When  the  pulley  is  in 
place  on  the  shaft,  bolted  up  as  one  piece,  it  is  subjected  to  the 
same  forces  as  the  simple  pulley.  Hence  its  general  design  fol- 


108 


MACHINE  DESIGN 


lows  the  same  principles,  and  we  need  only  study  the  fastening  of 
the  two  halves,  and  the  effect  of  this  fastening  on  the  detail  of  rim 
and  hub. 

The  simplest  stress  we  have  to  consider  on  the  rim  bolts  is 
one  of  pure  tension,  due  to  the  centrifugal  force  of  the  halves 
of  the  pulley,  A  safe  assumption  to  make  is  that  the  rim  is  free 


Fig.  24. 

from  the  arms  and  hub,  as  in  the  simple  pulley,  and  that  the  cen- 
trifugal force  developed  by  it  has  to  be  taken  by  the  rim  bolts 
alone.  In  other  words,  consider  the  rim  bolts  as  belonging  en- 
tirely to  the  rim,  and  make  them  as  strong  as  the  rim,  leaving  the 
hub  bolts  to  take  the  centrifugal  force  of  the  arms  and  hub,  and 
the  spreading  tendency  due  to  the  key. 

Another  tensile  stress  is  induced  in  the  rim  bolts  by  the  fact, 
that,  having  made  an  open  joint  in  the  rim,  and  in  addition  placed 
the  extra  weight  of  lugs  there,  the  centrifugal  action  at  this  point 
is  increased,  and  at  the  same  time  a  point  of  weakness 'in  the  rim 


109 


9G 


MACHINE  DESIGN 


introduced.  Referring  to  Fig.  24,  the  rim  flanges  EJ  tend  to  fly 
out  due  to  the  centrifugal  force  CF.  This  tends  to  open  the  joint 
J  at  the  outside  of  the  rim  ;  to  throw  a  bending  stress  on  the  rim, 
maximum  at  the  point  F  ;  and  to  "heel"  the  rim  flanges  about 
the  point  E.  The  rim  bolts  acting  on  the  leverage  c  about  the 
point  E  must  resist  these  tendencies,  and  are  thereby  put  in 
tension. 

Referring  to  equation  18,  we  find  the  intensity  of  stress  due  to 
the  centrifugal  force  of  the  rim  in  Ibs.  per  square  inch  to  be  : 


If  A  is  the  sectional  area  of  the  rim  in  square  inches,   this  means 
that   the  total   strength  of 
the   rim  is  represented    by 

— -•    The    strength    of    a 
bolt  is  represented  by  the 


expression  — -—•      If.  now, 

there  are  //  bolts  in  the 
iiange.  the  total  resisting 

forceof  the  bolts  is -; 

and  the  equation  represent- 
ing equality  of  strength  be- 
tween rim  and  bolts  is  : 

AV*  __  //sw;2 
To""    ^T^ 

from  which,  by  a  proper 
assumption  of  the  fiber 
stress  S,  which  should  be  Fi^'  ^ 

low.  the  opening-up  tendency  of  the  joint  being  neglected,  the  diam- 
eter at  the  root  of  the  thread  <7,  may  be  calculated,  and  the  nom- 
inal bolt  diameter  chosen.  Reference  to  the  table  for  strength 
of  bolts,  given  in  the  chapter  on  Bolts,  Studs,  etc.,  will  be  found 
convenient. 


110 


MACHINE  DESIGN  97 

It  is  very  doubtful  if  the  tension  on  the  flange  bolts,  due  to 
the  "  heeling"  about  E  can  be  calculated  with  sufficient  accuracy  to 
be  of  much  value.  It  is  probably  better  to  assume  S  at  a  low  value, 
say  4,000,  and,  in  addition,  for  large  and  high-speed  pulleys,  stif- 
fen the  rim  by  running  a  rib  between  the  flange  and  the  adjacent 
arm.  It  is  evident  that  if  we  make  the  rim  so  stiff  that  it  cannot 
deflect,  there  will  be  no  "  heeling "  about  E  ;  and  the  bolts  will 
be  well  proportioned  by  the  preceding  calculation,  giving  them 
equal  strength  to  that  of  the  rim  section. 

For  the  bolt  flange  itself,  any  tendency  to  open  at  the  joint  J 
would  cause  it  to  act  like  a  beam  loaded  at  some  point  near  its 
middle  with  the  bolt  load,  and  supported  at  J  and  E.  This 
condition  is  shown  in  Fig.  25.  Probably  the  weakest  section 
would  be  along  the  line  of  the  bolt  centers.  We  have  just  noted 

that  the  carrying  capacity  of  the  bolts  is .  '  •.  Hence,  assum- 
ing that  e  =  \f,  which  is  about  the  worst  case  which  could  hap- 
pen, we  have  a  beam  of  lengthy  loaded  at  the  middle  with  — 

and  supported  at  the  ends.  Equating  the  external  moment  to 
the  internal  moment,  we  have  : 

from  which  the  fiber  stress  *  in  the  flange  may  be  calculated  and 
judged  for  its  allowable  value. 

L,  maybe  assumed  a  little  narrower  than  the  pulley  face;  and 
t2  from  1  inch  to  2  inches  or  more,  depending  on  the  thickness  of 
the  rim. 

The  hub  bolts  doubtless  assist  the  rim  bolts  in  preventing 
the  halves  of  the  pulley  from  flying  apart.  They  also  clamp  the 
hub  tightly  to  the  shaft,  preventing  any  looseness  on  the  key. 
Their  function  is  a  rather  general  one;  and  the  specific  stress 
which  they  receive  is  practically  impossible  to  calculate.  As  a 
matter  of  fact,  if  the  hub  bolts  were  left  out  entirely,  the  pulley 
would  still  drive  fairly  well,  but  general  rigidity  and  steadiness 
would  be  impaired.  Hence  the  size  of  the  hub-  bolts  is  more  a 
practical  question  than  one  involving  calculation.  The  rim  bolts 


111 


OS  MACHINE  DESIGX 


should  be  figured  first,  and  their  size  determined  on;  then  the  hub 
bolts  CMII  be  judged  in  proportion  to  the  rim  bolts,  the  diameter  of 
shaft,  the  thickness  and  length  of  the  hub,  and  the  general  form 
of  the  pulley.  Often  appearance  is  the  deciding  factor,  it  being 
manifestly  inconsistent  to  associate  small  fastenings  with  large 
shafts  or  hubs,  even  though  the  load  be  actually  small. 

PRACTICAL  MODIFICATION.  Practical  considerations  are 
chiefly  responsible  for  the  locution  of  the  joint  in  a  split  pulley 
between  the  anus  instead  of  directly  at  the  end  of  an  arm.  where 
theoretically  it  would  seem  to  be  required.  It  is  usually  more 
convenient  in  the  foundry  and  machine  shop  to  have  the  joint  be- 
tween the  arms;  so  we  generally  find  it  placed  there,  and  strength 
provided  to  permit  this.  It  is  possible,  however,  to  provide  a 
double  arm,  or  a  single  split  arm,  in  which  case  the  joint  of  the 
pulley  comes  at  the  arm,  and  the  "heeling"  action  of  the  rim 
flanges  is  prevented. 

The  rim  bolts  should  be  crowde  I  as  close  as  possible  t>  the 
rim  in  order  to  reduce  the  stress  on  them,  and  also  the  stress  in 
the  flange  itself.  The  practical  point  must  not  be  forgotten,  how- 
ever that  the  bolts  must  have  sufficient  clearance  to  be  put  into 
place  beneath  the  rim. 

While  it  is  evident  that  the  rim  bolts  are  most  effective  in 
taking  care  of  the  centrifugal  action  of  the  halves,  yet  in  small 
split  pulleys  it  is  quite  common  to  omit  the  rim  bolts  and  to 
use  the  jub  bolts  for  the  double  purpose  of  clamping  the  shaft 
and  holding  the  two  halves  together.  The  pulley  is  cast  with  its 
rim  continuous  throughout  the  full  circle,  and  it  is  machined  in 
this  form.  It  is  then  cracked  in  two  by  a  well-directed  blow  of  a 
cold  chisel,  the  casting  being  especially  arranged  for  this  along  the 
division  line  by  cores  so  set  that  but  a  narrow  fin  of  metal  holds 
the  two  parts  together.  This  provides  sufficient  strength  for  cast- 
ing and  turning,  but  permits  the  cold  chisel  to  break  the  connec- 
tion easily. 

SPECIAL  FORflS  OF  PULLEYS. 

The  plain  cast-iron  pulley  has  been  used  in  the  foregoing 
discussion  as  a  basis  of  design.  A  pulley  is,  however,  such  a 
common  commercial  article,  and  finds  such  universal  use,  that 


MACHINE  DESIGN  99 

special  forms>  which  can  be  bought  in  the  open  market,  are  not 
only  cheaper  but  better  than  the  plain  cast-iron  pulley,  at  least  for 
regular  line-shaft  work. 

Cast  iron  is  a  treacherous  and  uncertain  material  for  rims  of 
pulleys.  It  is  not  wells.uited  to  high  fiber  stresses;  hence  the  range 
of  speed  permissible  for  pulley  rims  of  cast  iron  is  limited.  Steel 
and  wrought  iron,  having  several  times  the  tensional  strength  of 
cast  iron,  and  being,  moreover,  much  more  nearly  homogeneous 
in  texture,  are  well  suited  for  this  work;  one  of  the  best  pulleys  on 
the  market  consists  of  a  steel  rim  riveted  to  a  cast-iron  spider. 
Such  an  arrangement  combines  strength  and  lightness,  without 
increasing  complication  or  expense. 

The  all-steel  pulley  is  a  step  further  in  'this  direction.  Here 
the  rim,  arms,  and  hub  are  each  pressed  into  shape  by  specially 
devised  machinery,  then  riveted  and  bolted  together.  This  pulley 
is  strictly  a  manufactured  article,  which  could  not  compete  with  the 
simpler  forms  unless  built  in  large  quantities,  enabling  automatic 
machinery  to  be  used.  Large  numbers  of  pulleys  are  built  in  this 
way,  and  are  put  on  the  market  at  reasonable  prices. 

Wood-rim  pulleys  have  been  made  for  many  years,  and, 
except  for  their  clumsy  appearance,,  are  excellent  in  many  respects. 
The  rim  is  built  up  of  segments  in  much  the  same  way, as  an  ordi- 
nary pattern  is  made,  the  segments  being  so  arranged  that  they 
will  not  shrink- or  twist  out  of  shape  from  moisture.  The  hubs 
may  be  of  cast  iron,  bolted  to  wooden  webs,  and  carrying  hard- 
wood split  bushings,  which  may  be  varied  in  bore  within  certain 
limits  so  as  to  fit  different  sizes  of  shafting.  The  wooden  pulley 
is  readily  and  most  often  used  in  the  split  form,  thus  enabling  it 
to  be  put  in  position  easily  at  any  point  of  a  crowded  shaft.  It  is 
often  merely  clamped  in  place,  thus  avoiding  the  use  of  keys  or 
set  screws,  and  not  burring  or  roughening  the  shaft  in  any  way. 

PROBLEMS  ON  PULLEYS. 

1.  Calculate  the  tensile  stress  due  to  centrifugal    force  in 
the  rim  of  a  cast-iron  pulley  30  inches  in  diameter,  at  500  revolu- 
tions per  minute. 

2.  The  driving  force  of  a  belt  on  a  36-inch  pulley  is  800 
Jbs.,  and  the  belt  wrap  about  180°.     Calculate  proportions  of  el- 


100  MACHINE  DESIGN 

liptical  arms  to  resist  bending,  the  allowable  fiber  stress  being 
2,000. 

3.  A  pulley  12  inches  in  diameter.  j>-inch  web,  4- inch  diam- 
eter hub,  transmits  25  horse-power  at  a  belt  speed  of  3,000  ft. 
per  minute.     Calculate  the  maximum  shearing  stress  in  the  web. 

4.  In  Ficr.  24   assume  the  followino-  data:    L,  —- 1  inches: 

O  O  ! 

t.,=^\  inch;  e="L^  inches;  y=  3  inches;  area  of  rim  =  3  sq. 
in.;  allowable  tensile  stress  in  rim  1,000  Ibs.  per  sq.  in.  Calculate 
the  diameter  of  the  rim  bolts. 

o.  Calculate  the  fiber  stress  in  the  rim  bolt  flange  along  the 
line  of  the  bolts. 

SHAFTS. 

NOTATION— The  following  notation  is  used  throughout  the  chapter  ou  Shafts  : 

A,,  =  Angular  deflection  (degrees).  L  =  Length  along  shaft  (inches). 

H  =  Simple  bending  moment  (inch-lbs.).         LI,  L  '^Length  of  bearings  (inches.) 

Be= Equivalent   bending  moment  (inch-        M  =Distance  between  bearings  (feet.) 

N  =Number  of  revolutions  per  minute. 

c    ^Distance  from  neutral  axis  to  outer 

fiber  (toches).  =Driving  force  of  belt  (Ibs.). 

d.  do,  do,   da,   d4=Diameters    of    shaft  Pl=Load  applied  as  stated  (Ibs.). 

(inches).  R  =Radius  at  which  load  as  stated  acts 

di  =  Internal  diameter  of  shaft  (inches).  (inches). 

E=  Direct     modulus    of     elasticity    (a  S  =Fiber    stress,   tension,  compression, 
ratio).  or  shearing  (Ibs.  per-sq.  in.). 

c  =Transverse  deflection  (inches).  T  =Simple  twisting  moment  (inch-lbs.). 

G=Transverse  modulus  of  elasticity  (a  Te  =  Equivalent  twisting  moment  (inch- 
ratio).  lbs->- 

H=Horse-power  (33,000  ft.-lbs.  per  min-  Tn=Tension  in  tight  side  of  belt  (Ibs.). 

ute).  T,,=Tension  in  loose  side  of  belt  (Ibs.). 

I  =  Moment  of  inertia.  \V  =  Load  applied  as  stated  (Ibs.). 

K  =  Distance  between  bearings  (inches). 

ANALYSIS.  The  simplest  case  of  shaft  loading  is  shown  in 
Fig.  26.  The  equal  forces  W,  similarly  applied  to  the  disc  at  the 
distance  R  from  its  center,  tend  to  twist  the  shaft  off,  the  tendency 
being  equal  at  all  points  of  the  length  L  between  the  disc  and  the 
post,' to  which  the  shaft  is  rigidly  fastened.  The  fastening  to  the 
post,  of  course,  in  this  ideal  case,  takes  the  place  of  a  resisting 
member  of  a  machine.  A  state  of  pure  torsion  is  induced  in  the 
shaft;  and  any  element,  such  as  ca,  is  distorted  to  the  position  c-J, 
aob  being  the  angular  deflection  for  the  distance  L. 

The  case  of  Fig.  27  is  illustrative  of  what  occurs  when  a  belt 
pulley  is  substituted  for  the  simple  disc.  Here  the  twisting  action 
is  caused  by  the  driving  force  of  the  belt,  which  is  TD  -  T0  =  P. 


MACHINE  DESIGN 


101 


acting  at  the  radius  R.  Torsion  and  angular  deflection  exist  in 
the  shaft,  as  in  Fig.  26.  In  addition,  however,  another  stress  of 
a  different  kind  has  been  introduced;  for  not  only  does  the  shaft 
tend  to  be  twisted  off,  but  the  forces  Tn  and  T0,  acting  together, 
tend  to  bend  the  shaft,  the  bending  moment  varying  with  every 
section  of  the  shaft,  being  nothing  at  the  point  <?,  and  maximum 
at  the  point  c.  This  combined  action  is  the  most  common  of  any 
that  we  find  in  ordinary  machinery,  occurring  in  nearly  every  case 
with  which  we  have  to  deal. 

In  Fig.  27,  if  the  forces  Tn  and  T0  be  made  equal,  there  will 
be  no  tendency  at  all  to  twist  off  the  shaft,  but  the  bending  will 
remain,  being  maximum  at  the  point  c.  This  condition  is  illustra- 
tive of  the  case  of  all  ordinary  pins  and  studs  in  machines.  In 

this  sense,  a  pin  or  a  stud  is  sim- 
ply a  shaft  which  is  fixed  to  the 
frame  of  the  machine,  there  be- 
ing no  tendency  to  turning  of  the 
pin  or  stud  itself.  The  same 
condition  would  be  realized  if 
the  disc  in  Fig.  27  were  loose 
upon  the  shaft.  In  that  case, 
the  bending  moment  would  be 
caused  by  Tn  +  T0  acting  with 
the  leverage  L.  Of  course  there 
would  have  to  be  some  resistance 
for  Tn-T0  to  work  against,  in 
order  that  torsion  should  not  be 
transmitted  through  the  shaft. 

O 

This  condition  might  be  intro- 
Fig.  26.  duced  by  having  a  similar  disc 

lock  with  the  first  one  by  means 
of  lugs  on  its  face,  thus  receiving  and  transmitting  the  torsion. 

If  the  distance  L  becomes  very  great,  both  the  angular  deflec- 
tion due  to  twisting,  and  the  sidewise  deflection  due  to  bending, 
become  excessive,  and  not  permissible  in  good  design.  This 
trouble  is  remedied  by  placing  a  bearing  at  some  point  closer  to 
the  disc,  which,  as  it  decreases  L,  of  course,  decreases  the  bending 
moment  and  therefore  the  transverse  deflection.  The  angular  de- 


115 


102 


MACHINE  DESIGN 


flection  can  be  decreased  only  by  bringing  the  resistance  and  load 
nearer  together. 

The  above  implies,  of  course,  that  the  diameter  of  the  shaft  is  not 
changed,  it  being  obvious  that  increase  of  diameter  means  increase  of  strength 
and  corresponding  decrease  of  both  angular  and  transverse  deflection. 

If  the  speed  of  the  shaft  be  very  hifh,    and  the  distance  be- 

1  */  O 

tween  bearings,  represented  byL,  be  very  great,  the  shaft  will  take 
a  shape  like  a  bo\v  string  \vhen  it  is  vibrated.,  and  smooth  action 
cannot  be  maintained. 

It  is  necessary  to   carry  the  cases   of  Figs.   2*>    and   27  but  a 


Fig.  27. 

single  step  farther  to  illustrate  the  actual  working  conditions  of 
shafting  in  machines.  Suppose  the  rigid  post  to  have  the  shaft 
passing  clear  through  it.  and  to  act  as  a  bearing,  so  that  the  shaft 
can  freely  rotate  in  it,  the  resistance  being  exerted  somewhere  be- 
yond. The  twisting  moment  will  be  unchanged,  also  the  bending 
moment;  but  the  effect  of  the  bendino-  moment  will  be  on  each 

O 

particle  of  the  shaft  in  succession,  now  putting  compression  on  a 
given  particle,  and  then  tension,  then  compression  again,  and  so 
on.  a  complete  cycle  being  performed  for  each  revohitiou.  This 


MACHINE  DESIGN  103 


brings  out  a  very  important  difference  between  the  bending  stress 
in  pins  and  the  bending  stress  in  rotating  shafts.  In  the  one  case 
the  bending  stress  is  non  -re  versing;  in  the  other,  reversing;  and 
a  much  higher  fiber  stress  is  permissible  in  the  former  than  in  the 
latter. 

THEORY  —  Simple  Torsion.  In  the  case  of  simple  torsion 
the  stress  induced  in  the  shaft  is  a  shearing  one.  The  external 
moment  acts  about  the  axis  of  the  shaft,  or  is  a  polar  moment; 
hence  in  the  expression  for  the  moment  of  the  internal  forces,  the 
polar  moment  of  inertia  must  be  used.  Now,  from  mechanics  we 
have: 

T       SI' 
i-T' 

I          d3 
and  —  =  -=-y-    (for  circular  section  of  diameter  d)\ 

g^3 

therefore,  T  =  -g-p  (3°) 

from  which  the  diameter  for  any  given  twisting  moment  and  fiber 
stress  can  readily  be  found. 

For  a  hollow  shaft  this  expression  becomes: 


T 

Simple  Bending.  The  stresses  induced  in  a  pin  or  shaft  under 
simple  bending  are  compression  and  tension.  The  external  moment 
in  this  case  is  transverse,  or  about  an  axis  across  the  shaft;  hence 
the  direct  moment  of  inertia  is  applicable  to  the  equation  of  forces. 

B       SI- 

-D  =  -  > 

C 

I          d3 
and  —  =  jjy-jj  (for  circular  section  of  diameter  d)  ; 


therefore,  B  =  1O2'  (32) 

For  a  hollow  shaft  or  pin  this  expression  becomes: 

(33) 


Combined  Stresses.     In  the  greater  number  of  cases  met  with 


104 


MACHINE  DESIGN 


in  practice,  we  find  two  or  more  simple  stresses  acting  at  the  same 
time,  and,  although  the  shaft  may  be  strong  enough  for  any  one  of 
them  alone,  it  may  fail  under  their  combined  action.  The  most 
common  cases  are  discussed  below. 

Tension  or  Pressure  Combined  with  Bending.  In  Fig.  28, 
the  load  AV  produces  a  tension  acting  over  the  whole  area  of  d,  due 
to  its  direct  pull.  It  also  produces  a  bending  action  due  to  the 
leverage  II,  which  puts  the  fibers  at  B  in  tension  and  those  at  the 
opposite  side  in  compression.  It  is  evident,  therefore,  that  by 
taking  the  algebraic  sum  of  the  stresses  at  either  side  we  shall 
obtain  the  net  stress.  It  is  also  evident  that  the  greatest  and 


w 


Fig.  28.  Fig.  29 

controlling  stress  will  occur  on  the  side  where  the  stresses  add,   or 
on  the  tension  side.      Hence,  from  mechanics, 


or, 
Also, 


— Y    (due  to  direct  tension).      (34) 


WE  = 


10.2' 


10.2  WR  , 
or?  — TJ (due  to  bending).       (35) 

Tience  the  combined  tensional  stress  acting  at  the  point  B,  or,  in 


118 


MACHINE  DESIGN 


105 


fact,  at  any  point  on  the  extreme  outside  of  the  vertical  shaft  to- 
ward the  force  W,  is : 

c  _  4W  _j_  10'2  WR 
~  ird2 


(36) 


If  W  acted  in  the  opposite  direction,  the  greatest  stress  would 
still  be  at  the  side  B,  but  would  be  a  compression  instead  of  a  ten- 
sion, of  the  same  magnitude  as  before. 

Tension  or  Compression  Combined  with  Torsion.  In  Fig.  29, 
Y  might  be  the  end  load  on  a  vertical  shaft;  and  the  two  forces  W 
might  act  in  conjunction  with  it  as  in  the  case  of  Fig.  26,  at  the 
radius  R.  This  case  is  not  very  often  met  with.  It  is  usually 
possible  to  combine  the  moments,  find  an  equivalent  moment  of  a 
simple  kind,  and  use  the  corresponding  simple  fiber  stress.  In  the 
case  in  question  we  have  a  direct  stress  to  be  combined  with  a 
shearing  stress,  and  mechanics  gives  us  the  following  solution: 


Fig.  30. 

Let  Ss  =  simple  shearing  stress  (Ibs.  per  sq  in.). 
Let  Sc  =  simple  compressive  stress  (Ibs.  per  sq.  in.). 
Let  Srs=  resultant  shearing  stress  (Ibs.  per  sq.  in.). 
Let  Src=resultant  compressive  stress  (Ibs.  per  sq.  in.). 

We  then  have  : 


'  5.1  ' 

_  5.1(2WR) 
d3 


(37) 


Also, 


v 

V     = 


119 


100  MACHINE  DESIGN 


Sc  =      rV.  (38) 

Xow,  from  a  solution  given  in  simplest  form  in  "  Merriman's 
Mechanics"- — which  the  student  may  consult,  if  desired — values 
for  the  resultant  stresses  can  be  found.  Whichever  of  these  is 
the  critical  one  for  the  material  used,  should  form  the  basis  for  its 
diameter: 


(39) 


Also,  6^= -5  +  ^8.'+.  (40) 

Bending  Combined  with  Torsion.  In  Fig.  30,  the  load  W 
acts  not  only  to  twist  the  shaft  off. .  but  also  presses  it  sidewise 
against  the  bearing.  As  it  is  usually  customary  to  figure  the 
maximum  moment  as  taking  place  at  the  center  of  the  bearing, 
the  length  L.  which  determines  the  bending  moment,  is  taken -to 
that  point.  The  theory  of  the  stress  induced  in  this  case  is  com- 
plicated. In  order  to  make  the  magnitude  of  the  moments  clearer, 
let  us  introduce  the  two  equal  and  opposite  forces  F  and  F1,  each 
equal  to  W.  at  the  point  ('.  We  can  evidently  do  this  without 
changing  the  equilibrium  of  the  shaft  in  any  way.  We  now  see 
that  W  and  F1  act  as  a  couple  giving  a  twisting  moment  WR  ; 
and  that  F  acts  with  a  leverage  L,  producing  a  bending  moment 
FL  =  WL,  at  the  middle  of  the  bearing. 

If.  now,  we  find  an  equivalent  twisting  moment,  or  an  equiv- 
alent bending  moment,  which  would  produce  the  same  effect  on 
the  fibers  of  the  shaft  as  the  two  combined,  we  can  treat  the  cal- 
culation of  the  diameter  as  a  simple  case,  and  proceed  as  in  the 
cases  of  simple  torsion  and  simple  bending  considered  above.  This 
relation  is  given  us  in  mechanics: 


(42) 


These  expressions  are  true  in  relation  to  each  other,  on  the  assump- 
tion that  the  allowable  fiber  stress  S  is  the  same  for  tension,    com- 


120 


MACHINE  DESIGN  107 


pression,  and  shearing.  For  the  material  of  which  shafts  are  usu- 
ally made,  this  is  near  enough  to  the  truth  to  give  safe  and  practi- 
cal results.  Using  the  expressions  for  internal  moments  of  resist- 
ance as  previously  noted  for  circular  sections,  we  then  have  : 

jz 

(43) 

Also,  T.=  (44) 

Either  equation  may  be  used  ;  the  diameter  d  will  result  the  same 
whichever  equation  is  taken.  For  the  sake  of  simplicity,  equation 
42  is  generally  preferred,  equation  44  being  taken  in  conjunction 
with  it. 

The  expression  1/B2  +  T2  is  one  that  would  be  a  long  and 
tedious  task  to  calculate.  By  inspection  it  is  readily  seen  that 
this  quantity  can  be  graphically  represented  by  means  of  a  right- 
angled  triangle  having  B  and  T  as  the  sides.  We  may  then  lay 
down  on  a  piece  of  paper,  to  some  convenient  scale,  the  moments 
B  and  T  as  the  sides  of  a  right-angled  triangle,  when,  upon 
measuring  the  hypothenuse,  we  can  easily  read  off  to  the  same 
scale  1/B2  +  I"2.  Even  if  the  drawing  is  made  to  a  small  scale, 
the  accuracy  of  the  reading  will  be  sufficient  to  enable  the  value 
for  d  to  be  solved  very  closely.  This  graphical  method  is  illus- 
trated in  Part  I. 

Deflection.  For  a  shaft  subjected  to  pure  torsion,  as  in  Fig. 
26,  the  angular  deflection  due  to  the  load  may  be  carried  to  a  cer- 
tain point  before  the  limit  of  working  fiber  stress  is  exceeded. 
The  equation  worked  out  from  mechanics  for  this  condition,  is: 

584  TL 
A  =    -->  (45) 


which  at  once  gives  the  number  of  degrees  of  angular  deflection 
for  a  shaft  whose  modulus  of  elasticity,  torsional  moment,  and 
length  are  known. 

The  shearing  modulus  of  elasticity  of  ordinary  shaft  steel  runs  from 
10,000,000  to  13,000,000,  giving  as  an  average  about  12,000,000. 

By  the  welLknown  relation  of  "  Hooke's  law  "  (stresses  pro- 
portional to  strains  within  the  elastic  limit  of  the  material),  we  have: 


121 


10S  MACHINE  DESIGN 


A°          SL  . 
300°  r~  TrG^' 

A?rG^ 
"WIT  (46) 

A  twist  of  one  degree  in  a  length  of  twenty  diameters  is  a 
usual  allowance.  Substituting  A  =  1,  L  =  20d,  and  G  =  12,000, 
000.  we  have: 

S  =  5,240  (nearly).  (47) 

This  is  a  safe  value  for  shearing  fiber  stress  in  steel.  In  fact,  in 
calculations  for  strength,  even  for  reversing  stresses,  the  usual 
figure  is  8.000  (Ibs.  per  square  inch),  thus  indicating  that  the  re- 
lation of  one  degree  to  twenty  diameters  is  well  within  the  limit 
of  strength. 

for  a  hollow  shaft  the  above  formula  becomes  : 

584  TL 

A°-a,vz*     ./n-  (48) 


Transverse  deflection  occurs  when  the  shaft  is  subjected  to  a 
bending  moment.  It  may  therefore  exist  alone  or  in  conjunction 
with  angular  deflection.  Transverse  deflection  of  shafts,  however, 
rarely  exists  u]>  to  the  point  of  limiting  fiber  stress,  because  before 
that  point  is  reached  the  alignment  of  the  shaft  is  so  disturbed 
that  it  is  not  practicable  as  a  device  for  transmitting  power.  A 
transverse  deflection  of  .01  inch  per  foot  of  length  is  a  common 
allowance  ;  but  it  is  impossible  to  fix  any  general  limit,  as  in  many 
cas'js  this  figure,  Jf  exceeded,  would  do  no  harm,  while  in  others — 
such  as  heavily  loaded  or  high-speed  bearings — even  the  figure 
given  might  be  fatal  to  good  operation. 

The  formula  for  transverse  deflection,  deduced  from  mechan- 
ics, varies  with  the  system  of  loading.  The  three  'most  common 
conditions  only  are  given  below,  reference  to  the  handbook  being 
necessary  if  other  conditions  must  be  satisfied: 

Fixed  at  one  end,  loaded  at  ttie  other, 

•" 

(49)    - 


122 


GENERAL  ARRANGEMENT  OF  JONVAL  TURBINE. 

Central  Engineering  Works,  Oldham,  Eng. 


MACHINE  DESIGN  109 


Supported  at  ends,  loaded  in  middle, 

WL3 

*  =  48ET  (50) 

Supported  at  ends,  loaded  uniformly, 

_5WL» 

~  384  El"  ^^ 

For  transverse  deflection  the  direct  modulus  of  elasticity  must 
be  used,  for  the  fibers  are  stretched  or  compressed,  instead  of  being 
subjected  to  a  shearing  action.  The  most  usual  value  of  the  di- 
rect modulus  of  elasticity  for  ordinary  steel  is  30,000,000,  and  is 
denoted  in  most  books  by  the  symbol  E.  Both  the  shearing  and 
direct  moduli  of  elasticity  are  really  nothing  but  the  ratio  of  the 
stress  to  the  strain  produced  by  that  stress,  it  being  assumed  that 
the  given  material  is  perfectly  elastic.  A  material  is  supposed  to 
be  perfectly  elastic  up  to  a  certain  limit  of  stress,  and  it  is  within 
this  limit  that  the  relation  as  above  holds  good. 

Expressed  in  the  form  of  an  equation  this  would  be  : 


Centrifugal  Whirling.  If  a  line  shaft  deflect  but  slightly, 
due  to  its  own  weight,  or  the  weight  or  pressure  of  other  bodies 
upon  it,  and  then  be  run  at  a  high  speed,  the  centrifugal  force  set 
up  increases  the  deflection,  and  the  shaft  whirls  about  the  geomet- 
rical line  through  the  centers  of  the  bearings,  causing  vibration 
and  wear  in  the  adjoining  members.  It  is  evident  that  the  prac- 
tical remedy  for  this  tendency  in  a  shaft  of  given  diameter  and 
speed  is  to  locate  the  bearings  sufficiently  close  to  render  the  action 
of  small  effect. 

Many  formulae  might  be  given  for  this  relation,  each  being 
based  on  different  assumptions.  Perhaps  as  widely  applied  and 
as  simple  as  any,  is  the  "  Rankine  "  formula,  which  sets  the  limit 
of  length  between  bearings  for  shafts  not  greatly  loaded  by  inter- 
mediate pulleys  or  side  strains  : 


M  -175   J^--  (53) 


123 


110 


MACHINE  DESIGN 


Horse=Power  of  Shafting.  Horse-power  is  a  certain  specific 
rate  of  doing  work,  ?;/.?.,  33,000  foot-pounds  per  minute.  Hence, 
to  find  the  horse-power  that  a  shaft  will  transmit,  we  must  first 
find  the  work  done,  and  then  relate  it  to  the  speed.  Take,  for  ex- 
ample, the  case  of  a  pulley,  the  symbols  being  the  same  as  before 

namely,  P-- driving  force  at  rim  of  pulley  (Ibs.);  R  —  radius 

of  pulley  (inches) ;  N  =  number  of  revolutions  per  minute;  and 
II  —  horse-power.      Then. 

Work  —  force  X  distance  =  P  X  (2  IT  RX)  =  II   X  33,000  X  12; 

63,02511 

PR-     -^ (54) 


This  is  one  of  the  most  useful  equations  for  calculations  involving 
horse -power.  P>y  it  the  number  of  inch-pounds  torsion  for  any 
horse-power  can  be  at  once  ascertained. 

It  should  be  clearly  noted,  however,  that  in.  this  equation  the 
bending  moment  does  not  enter  at  all.  Hence  any  shaft  based  in 
size  on  JioTse-power  alone,  is  based  on  torsional  -moment  alon-e, 
bending  moment  being  entirely  neglected.  In  many  cases  the 
bending  moment  is  the  controlling  one  as  to  limiting  fiber  stress. 
Hence  empirical  shafting  formulae  depending  upon  the  horse- 
power relation  are  unsafe,  unless  it  is  definitely  known  just  what 
torsional  and  bending  moments  have  been  assumed. 

The  only  safe  way  to  figure  the  size  of  a  shaft  is  to  find 
accurately  what  torsional  moment  and  bending  moment  it  has  to 
sustain,  and  then  combine  them  according  to  equation  41  or  42 


124 


MACHINE  DESIGK  111 

introducing  the  element  of  speed  as  basis  for  assumption  of  a  high 
or  .low  working  fiber  stress. 

PRACTICAL  MODIFICATION.  The  practical  methods  of 
handling  the  theoretical  shaft  equations  have  reference  to  the  fit  of 
the  shaft  within  the  several  pieces  upon  it.  The  running  fit  of  a 
shaft  in  a  bearing  is  usually  considered  to  be  so  loose  that  the  shaft 
could  freely  deflect  to  the  center  of  the  bearing.  'This  is  doubtless 
an  extreme  view  of  the  case,  but  it  is  the  only  safe  assumption. 
Hence  a  shaft  running  in  bearings  (see  Fig.  31)  is  supposed  to  be 
supported  at  the  centers  of  those  bearings,  and  its  theoretical 
strength  is  based  on  this  supposition. 

For  a  tight  or  driving  fit  upon  the  shaft,  a  safe  assumption  to 
make  is  that  there  is  looseness  enough  at  the  ends  of  the  fit  to  per- 
mit the  shaft  to  be  stressed  by  the  load  a  short  distance  within  the 
faces  of  the  hub,  say  from  ^  inch  to  1  inch.  For  example,  refer- 
ring to  Fig.  31,  suppose  P>  to  be  the  transverse  load,  exerted 
through  a  hub  fast  upon  the  part  of  the  shaft  d3.  Taking  mo- 
ments about  the  center  of  one  bearing,  and  solving  for  the  reaction 
at  the  center  of  the  other,  we  have  : 


(55) 


Also,  P,  t  =  R2  K; 

K^TT 

Now,  as  far  as  the  part  of  shaft  d3  is  concerned,  it  may  depend  for 
It:  size  on  the  bending  moment  R2  J,  or  on  Rj  a.  The  reason  the 
lever  arm  is  not  taken  to  the  point  directly  under  the  load  P,,  is 
because  it  is  not  practically  possible  to  break  the  shaft  at  that 
point,  on  account  of  the  reinforcement  of  the  hub,  which  is  tightly 
fitted  upon  it.  Trying  these  moments  to  see  which  is  the  greater,' 
we  shall  find  that  the  greater  moment  always  occurs  in  connection 
with  the  longer  lever  arm.  Hence  R2  I  will  be  greater  than  Rt  a. 
We  then  write  the  equation  of  external  moment  =  internal  mo- 
ment: 

Sd33 
R'6  ~:  T02"' 


125 


112  MACHINE  DESIGN 


4  =  NI^-  (57) 

For  the  size  of  bearing  A  we  have  the  maximum  bending  HID- 
ment: 

,   LI       Sd* 


i 

or,  dt=^ g-gi-  (58) 

For  the  size  of  bearin     B  we  have  the  maximum  moment: 


10.2  ' 

4^  '  <59) 

The  above  calculations  are,  of  course,  on  the  assumption  that  no  torsion 
is  transmitted  either  way  through  this  axle.  We  should  in  that  case  have 
combined  torsion  and  bending.  This  has  been  made  sufficiently  clear,  in  pre- 
ceding paragraphs  and  in  Part  I,  to  require  no  further  illustration. 

The  dotted  line  in  Fig.  81  shows  the  theoretical  shape  the 
axle  should  take  under  the  assumed  conditions.  The  practical 
modification  of  this  shape  is  obvious.  At  the  shoulders  of  the 
shaft  the  corners  should  not  be  sharp,  but  carefully  filleted,  to 
avoid  the  possible  starting  of  a  crack  at  those  points. 

Often  the  diameter  of  certain  parts  of  a  shaft  may  be  larger 
than  strength  actually  calls  for.  For  example,  in  Fig.  81,  the 
part  c7:i  need  only  be  as  large  as  the  dotted  line;  but  it  is  obvious 
that  unless  the  key  is  sunk  in  the  body  of  the  shaft,  the  hub  could 
not  be  slipped  into  place  over  the  part  </4.  If,  however,  the  diam- 
eter r/3  be  made  large  enough  so  that  the  bottom  of  the  key  will 
clear  r74,  the  rotary  cutter  which  forms  the  key  way  in  r73  will  also 
clear  *74,  and  the  key  way  can  be  more  easily  produced. 

In  cases  where  fits  are  not  required  to  be  snug,  a  straight 
shaft  of  cold-rolled  steel  is  commonly  used.  Here  any  parts  fast- 
ened on  the  middle  of  the  shaft  have  to  be  driven  over  a  consider- 
able length  of  the  shaft  before  they  reach  their  final  position. 
Moreover,  there  is  no  definite  shoulder  to  stop  against,  and  meas- 
urement has  to  be  resorted  to  in  locating  them. 


126 


MACHINE  DESIGN  113 

It  does  not  pay  to  turn  any  portion  of  a  cold-rolled  shaft,  un- 
less it  be  the  very  ends,  for  relieving  the  "  skin  tension  "  in  such 
material  is  sure  to  throw  the  shaft  out  of  line  and  necessitate 
subsequent  straightening. 

Turned-steel  shafts  for  machines  may  with  advantage  be 
slightly  varied  in  diameter  wherever  the  fit  changes;  and  although 
the  production  of  shoulders  costs  something,  yet  it  assists  greatly 
in  bringing  the  parts  to  their  exact  location,  and  enables  the  work- 
man to  concentrate  his  best  skill  on  the  fine  bearing  fits,  and  to 
save  time  by  rough -turn  ing  the  parts  that  have  no  fits. 

Hollow  shafts  are  practicable  only  for  large  sizes.  The  advan- 
tages of  removing  the  inner  core  of  metal,  aside  from  some  specific 
requirement  of  the  machine,  are  that  it  eliminates  all  possibility  of 
cracks  starting  from  the  checks  that  may  exist  at  the  center,  per- 
mits inspection  of  the  material  of  a  shaft,  and,  in  case  of  hollow- 
forged  shafts,  gives  an  opening  for  the  forging  mandrel.  In  the 
last  case,  the  material  is  improved  by  a  rolling  process. 

The  material  most  common  for  use  in  machine  shafting  is  the 
ordinary  "  Machinery  Steel,"  made  by  the  Bessemer  process.  This 
steel  is  apt  to  be  "seamy,"  and  often  contains  checks  and  flaws 
that  are  detected  only  upon  sudden  and  unexpected  breakage  of  a 
part  apparently  sound.  This  characteristic  is  a  result  of  the  proc- 
ess employed  in  the  manufacture  of  the  steel,  and  thus  far  has 
never  been  Wholly  eliminated.  Bessemer  steel  is,  nevertheless,  a 
very  useful  material,  and  the  above  weakness  is  not  so  serious  but 
that  this  kind  of  steel  can  be  used  with  success  in  the  great  majority 
of  cases. 

When  a  more  homogeneous  shaft  is  desired,  open=hearth  steel 
is  available.  This  is  a  more  reliable  material  to  use  than  the  Bes- 
semer, and  costs  somewhat  more.  It  makes  a  stiff,  true,  fine-sur- 
faced shaft,  high-grade  in  every  respect.  It  is  usually  specified 
for  armature  shafts  of  dynamos  and  motors. 

Steels  of  special  strength,  toughness,  and  elasticity  are  made 
under  numerous  processes.  Nickel  steel  is  perhaps  the  most  con- 
spicuous example.  While  for  this  steel  a  high  price  has  to  be 
paid,  yet  its  great  strength,  in  connection  with  other  valuable  qual- 
ities, makes  it  a  material  extremely  valuable  for  service  where  light 
weight  is  essential,  or  where  contracted  space  demands  small  size. 


127 


114  MACHINE  DESIGN 


The  range  of  strength  of  these  various  steels  is  so  great  that  it  is  well- 
nigh  iseless  to  go  into  a  discussion  of  it  here.  "Reference  should  be  had  to 
the  t  tended  discussions  of  the  handbooks,  and  to  special  trade  pamphlets. 
A  st  ly  of  the  possibilities  of  steel  in  its  various  forms  for  use  in  shafting, 
is  vc  -  valuable  as  a  basis  for  design,  as  it  can  almost  be  said  that  a  machine 
consi  ts  chiefly  of  a  "collection  of  shafts  with  a  structure  built  round  them." 
The  lafts  are  like  a  core,  and  evidently  the  size  of  the  core  determines  the 
shell  about  it. 

PROBLEHS  ON  SHAFTS. 

1.  Required  the  twisting  moment  on   a  shaft  that  transmits 
30  horse-power  at  120  revolutions  per  minute. 

2.  Find  the  diameter  of  a  steel  shaft  designed  to  transmit  50 
horse-power  at  150  revolutions  per  minute. 

3.  Assuming  same  data  as  in  Problem  1,  find  the  diameters 
of  a  hollow  shaft  for  a  value  of  S  —  8,000. 

4.  A   belt   on    an    idler  pulley   embraces   an    angle   of    120 
degrees.      Assuming  tension    of  belt    1,000  pounds  on  each  side, 
and  pulley  located  midway  between  bearings,  which  are  30  inches 
from  center  to  center,  what  is  the  diameter  of  shaft  required  '. 

5.  ( 'alculate  the  diameter  of  a  steel  shaft  designed  to  transmit 
a    twisting   moment   of  400.000    inch-pounds  and  also   to  take  a 
bending  moment  of  300,000  inch-pounds. 

G.  Find  the  angular  deflection  in  a  4-inch  shaft  20  feet  long 
when  subjected  to  a  load  of  5,500  pounds  applied  to  an  arm  of 
30-inch  radius.  Assume  transverse  modulus  of  elasticity  equal  to 
12,000.000. 

7.  The  overhung  crank  of  a  steam  engine  has  a  force  of 
32,000  Ibs.  at  the  center  of  the  crank  pin.  which  is  12  inches  from 
the  center  of  the  shaft  bear  in  tr,  measured  parallel  to  the  shaft. 
The  radius  of  crank  arm  is  10  inches.  Assume  S  equal  to  10,000. 
Calculate  the  diameter  of  the  crank  shaft. 

S.  On  'a  short,  vertical  steel  shaft  the  load  is  5,000  pounds. 
A  gear,  36  teeth,  1^  diametral  pitch,  at  top  of  shaft,  transmits  a 
load  of  4,000  pounds  at  the  pitch  line.  Safe  shear  —  7,500.  What 
is  the  diameter  of  the  shaft  ? 

SPUR  GEARS. 

NOTATION— The  following  notation  is  used  throughout  the  chapter  on  Spur  Gears: 

6  =Breaclth  of -rectangular  section  of       M.  Mi-Revolutions  per  minute. 

arm  (inches).  jU,= Coefficient  of  friction  between  teeth. 


128 


MACHINE  DESIGN  115 

C  =  Width   of   arm    extended  to  pitch     .  N=Number  of  teeth, 

line  (inches).  M  =  Number  of  arms. 

c  =Distancefrom  neutral  axis  to  outer  P=Diametral  pitch  (teeth  per  inch  of     . 

fiber  (inches).  diameter). 

D=Pitch  diameter  of  gear  (inches).  P'=Circular  pitch  (inches). 

F=Face  of  gear  (inches).  Q,  Qi=Normal  pressure  between  teeth 
f  =Clearance     of     tooth    at     bottom  (Ibs.). 

(inches).  R,Ri=Resultant,      pressure      between 
G=Thickness  of  arm  extended  to  pitch  teeth  (Ibs.). 

line  (inches).  ,-,  n= Radius  of  pitch  circles  (inches). 

H=Thickness  of  tooth  at  any  section  s  =  Fiber   stress   of  material  (Ibs.  per 

(inches).  sq.  in.). 

7i  =  Depth  of  rectangular  section  of  arm  s  =  Addendum    of    tooth  (inches)  =De- 

(inches).  dendum  of  tooth. 

I  =Moment  of  inertia.  t  ^Thickness   of   tooth   at   pitch   line 
'K= Thickness  of  rim  (inches).  (inches). 

L=  Distance  from  top  of  tooth  to  any  w=Load  at  pitch  line  (Ibs.). 

section  (inches).  y  ^Coefficient  for  "  Lewis  "  formula. 

ANALYSIS.  If  a  cylinder  be  placed  on  a  plane  surface,  with 
its  axis  parallel  to  the  plane,  an  attempt  to  rotate  the  cylinder 
about  its  axis  would  cause  it  to  roll  on  the  plane. 

Again,  if  two  cylinders  be  provided  with  axial  bearings,  and 
be  slightly  pressed  together,  motion  of  one  about  its  axis  will 
cause  a  similar  motion  of  the  other,  the  two  surfaces  rolling  one 
on  the  other  at  their  common  tangent  line.  If  moved  with  care, 
there  will  be  no  slipping  in  either  of  the  above  cases — which  is 
explained  by  the  fact  that  no  matter  how  smooth  the  surfaces  may 
appear  to  be,  there  is  still  sufficient  roughness  to  make  the  little 
irregularities  interlock  and  act  like  minute  teeth. 

The  magnitude  of  the  force  possible  to  be  transmitted  de- 
pends not  only  on  the  roughness  of  the  surfaces,  but  on  the 
amount  of  pressure  between  them.  Suppose  that  one  cylinder  is 
a  part  of  a  hoisting  drum,  on  which  is  wound  a  rope  with  a  weight 
attached.  We  can  readily  make  the  weight  so  great  that,  no  mat- 
ter how  hard  we  press  the  two  cylinders  together,  the  driving 
cylinder  will  not  turn  the  hoisting  cylinder,  but  will  slip  past  it. 
If  now,  instead  of  increasing  the  pressure,  which  is  detrimental 
both  to  cylinders  and  bearings  of  same,  we  increase  the  coarseness 
of  the  surfaces,  or,  in  other  words,  put  teeth  of  appreciable  size 
on  these  surfaces,  we  attain  the  desired  result  of  positively  driving 
without  excessive  side  pressure. 

These  artificial  projections,  or  teeth,  must  fit  into  one  another; 
hence  the  surfaces  of  the  original  cylinders,  having  been  broken 
up  into  alternate  projections  and  hollows,  have  entirely  disap- 


129 


110 


MACHINE  DESIGN 


peared  to  the  eye;  they  nevertheless  exist  as  ideal  or  imaginary 
surfaces,  which  roll  together  with  the  same  surface  velocities  as  if 
in  bodily  form,  provided  that  the  curves  of  the  teeth  are  correctly 
formed.  Several  mathematical  curves  are  available  for  use  as 
tooth  outlines,  but  in  practice  the  involute  and  cycloidal  curves 
are  the  only  ones  used  for  this  purpose. 

The  ideal  surfaces  are  known  as  pitch  cylinders  or  pitch 
circles.  In  Fig.  32  is  shown  an  end  view  of  such  a  pair  of  cylin- 
ders in  contact  at  their  pitch  point  P.  In  gear  calculations  we 
assume  that  there  is  no  slip,  between  the  pitch  circles,  acting  as 
driving  cylinders;  hence  the  speeds  of  the  two  pitch  circles  at  the 


pitch  point  are  equal.      If  M  and  Mt  he  the  revolutions  per  minute 
of  the  cylinders  respectively,  /'  and  i\  their  radii,  then 


M 


That  is,  the  number  of  revolutions  varies  inversely  as  the  radii. 

The  simple  calculation  as  above  is  the  key  to  all  calculations 
involving  gear  trains  in  reference  to  their  speed  ratio. 

Fig.  33  represents  cycloidal  teeth  in  the  two  extreme  positions 
of  beginning  and  ending  contact.  The  normal  pressure  Q  or  Qx 
between  the  teeth  in  each  position  acts  through  the  pitch  point  O, 
as  it  must  always  do  in  order  to  insure  the  condition  of  ideal  roll- 


ISO 


MACHINE  DESIGN 


117 


ing  of  the  pitch  circles,  and  the  velocity  ratio  proportional  to  — 

As  the  surfaces  of  the  teeth  slide  together,  frictional  resistance  is 
produced  at  their  point  of  contact.  This  force  is  widely  variable, 
depending  on  the  material  and  condition  of  the  tooth  surfaces, 
whether  smooth  and  well  lubricated,  or  rough  and  gritty.  As  this 
resistance  acts  in  conjunction  with  the  normal  force  between  the 
teeth,  we  may  construct  a  parallelogram  of  forces  on  these  two  as 
a  base,  the  resultant  pressure  between  the  teeth  being  slightly 
changed  thereby,  as  shown  in  Fig  33. 

Assuming  a  coefficient  of  friction  fJ,,  the  force  of  friction  is  /A  Q  or  p  Qi 
and  the  resultant  pressure  R  or  Ri. 

Tooth  B  of  the  FOLLOWER  is  therefore  under  a  heavy  bending  moment 
measured  by  the  product  RL,  L 
being  the  perpendicular  distance 
from  the  center  of  the  tooth  at 
its  base  to  the  line  of  the  force. 
This  tooth  also  has  a  relatively 
small  compressive  stress  due  to 
the  resolved  part  of  R  along  the 
radius,  and  a  relatively  small 
shearing  stress  due  to  the  re- 
solved part  of  R  along  a  tangent 
to  the  pitch  circle. 

Tooth  D  of  the  driven  wheel 
or  FOLLOWER  has  a  relatively 
large  shearing  stress,  a  small 
bending  .  moment,  and  practi- 
cally no  direct  compressive 


Tooth  A  of  the  driving  wheel 
or  DRIVER  has  a  relatively  large 
shearing  stress,  a  small  bending  moment,  and  small  compressive  stress. 

Tooth  C  of  the  DRIVER  has  a  large  bending  moment,  but  small  com 
pressive  and  shearing  stresses. 

The  conditions  as  noted  above  are  not  those  of  every  pair  of 
gears,  in  fact  they  vary  with  every  difference  of  pitch  circle,  or  of 
detail  and  position  of  tooth.  It  is  true,  however,  that  in  nearly 
all  cases  in  practice  the  bending  stress  is  the  controlling  one  from 
a  theoretical  standpoint.  Moreover,  the  designer  must  consider 
the  form  and  strength  of  the  tooth  when  it  is  under  the  condition 
of  maximum  moment.  This  evidently,  from  the  above,  occurs  at 
the  beginning  of  contact,  for  the  follower  teeth;  and  at  the  end  of 
contact,  for  the  driver  teeth.  In  the  particular  case  illustrated  in 


131 


us 


MACHINE  DESIGN 


Fig.  8-5,  if  the  material  in  both  gears  were  the  same,  tooth  C, 
being  the  weaker  at  the  root,  would  probably  break  before  B;  but 
if  C  were  of  steel,  and  B  of  cast  iron,  B  might  break  first. 

It  will  be  noticed  that  E,  is  nearly  parallel  to  the  top  of  the 
tooth;  and  it  may  easily  happen  that  the  friction  may  become  of 
such  a  value  that  it  will  turn  the  direction  of  R  until  it  lies  along 
the  top  of  the  tooth  exactly,  which  is  the  condition  for  maximum 
moment.  For  strength  calculations  it  is  usual  to  consider  this 
condition  as  existing  in  all  cases. 

At  the  beginning  of  contact  there  is  more  or  less  shock  when 
the  teeth  strike  together,  and  this  effect  is  much  more  evident  at 
hio'h  speeds.  There  is  also  at  the  beginning  of  contact  a  sort  of 

C         i  o  o 

chattering  action  as  the  driving  tooth  rubs  along  the  driven  tooth. 

Uniform  distribution  of  pressure  along  the  face  of  the  tooth  is 
often  impaired  by  uneven  wear  of  the  bearings  supporting  the  gear 
shafts,  the  pressure  being  localized  on  one  corner  of  the  tooth.  The 
same  effect  is  caused  by  the  accidental  presence  of  foreign  material 
between  the  teeth.  Again,  in  cast  gearing,  the  spacing  may  be 
irregular,  or.  on  account  of  draft  on  the  pattern,  the  teeth  may  bear 
at  the  high  points  only.  "While  it  is 
usual  to  consider  that  the  load  is  evenly 
distributed  along  the  face  of  the  tooth, 
yet  the  above  considerations  show  that 
mi  ample  margin  of  strength  must  al- 
ways !>•'  all  meed  on  account  of  these 
uncertainties. 

"When  the  number  of  teeth  in  the 
mating  gears  is  high,  the  load  will  be 
distributed  between  several  teeth  ;  but, 
as  it  is  almost  certain  that  at  some  time 
the  proper  distribution  of  load  will  not 

exist,  and  that  one  tooth  will  receive  the  full  load,  it  is  considered 
that  practically  the  only  safe  method  is  so  to  design  the  teeth  that 
a  single  tooth  may  be  relied  upon  to  withstand  the  full  load  without 
failure. 

THEORY.  Based  on  the  Analysis  as  given,  the  theory  of  gear 
teeth  assumes  that  one  tooth  takes  the  whole  load,  and  that  this  load 
is  evenly  distributed  along  the  top  of  the  tooth  and  acts  parallel  with 


Fig.  34. 


132 


MACHINE  DESIGN  119 


?ts  base,  thus  reducing  the  condition  of  the  tooth  to  that  of  a 
cantilever  beam.  The  magnitude  of  this  load  at  the  top  of  the 
tooth  is  taken  for  convenience  the  same  as  the  force  transmitted  at 
the  pitch  circle.  This  condition  is  shown  in  Fig.  34.  Equating 
the  external  moment  to  the  internal  moment,  we  then  have,  from 
mechanics: 


The  thickness  II  is  usually  taken  either  at  the  pitch  line  or  at 
the  root  of  the  tooth  just  before  the  fillet  begins;  and  L,  of 
course,  is  dependent  on  the  tooth  dimensions.  The  formula  is 
most  readily  used  when  the  outline  of  the  tooth  is  either  assumed 
or  known,  a  trial  calculation  being  made  to  see  if  it  will  stand  the 
load,  and  a  series  of  subsequent  calculations  followed  out  in  the 
same  way  until  a  suitable  tooth  is  found.  This  method  is  pursued 
because  there  are  certain  even  pitches  which  it  is  desirable  to  use; 
and  it  is  safe  tc  say  that  any  calculation  figured  the  reverse  way 
would  result  in  fractional  pitches.  The  latter  course  may  be  used, 
however,  and  the  nearest  even  pitch  chosen  as  the  proper  one. 

As  stated  under  "Analysis,"  there  are  a  great  many  circum- 
stances attending  the  operation  of  gears  which  make  impossible 
the  purely  theoretical  application  of  the  beam  formulae.  For  this 
reason  there  is  no  one  element  of  machinery  which  depends  so 
much  on  experience  and  judgment  for  correct  proportion  as  the 
tooth  of  a  gear.  Hence  it  is  true  that  a  rational  formula  based  on  • 
the  theoretical  one  is  really  of  the  greater  practical  value  in  tooth 
design. 

If  we  examine  formula  61,  we  find  that  in  a  form  solved  for 
W,  we  have: 

•W=»£.  (6,)-'. 

Of  these  quantities,  H  and  L  are  the  only  variables,  for  we  can 
make  the  others  what  we  choose.  II  and  L  depend  upon  the 
circular  pitch  P1  and  the  curvature  and  outline  of  the  tooth.  If 
now  we  could  settle  or>  a  standard  system  of  teeth,  we  could  estab- 
lish a  coefficient  to  ba  used  to  take  the  place  of  the  variable  part 


133 


120  MACHINE  DESIGN 


of  II  and  L,  which  depends  on  the  outline  of  tooth,  and  we  should 
thus  have  an  empirical  formula  which  would  be  on  a  theoretical 
basis. 

This,    3Ir.    "Wilfred  Lewis  has  done;    and   it   is    safe  to  say 
that  this  formula  is  more  universally  used  and  with  more  satis- 


factory  practical  results  than  any  other  formula,  theoretical  or 
practical,  that  has  ever  been  devised.  His  coefficient  is  known  as 
//,  and  was  determined  from  many  actual  drawings  of  different 
forms  of  teeth  showing  the  weakest  section.  This  coefficient  is 
worked  out  for  the  three  most  common  systems  as  follows: 

0  01° 
For  2CP  involute,     y  =  0.154   -    -T^— 

For  1-V  involute  0.684 

and  ccloidal      ^'  =  °-m    ' 


For  radial  flanks,  //  =  0.075  -   -1= —  (65) 

The  tooth  upon  which  the  above  is  based  is  the  American  standard  or 
Brown  &  Sharpe  tooth,  for  which  the  proportions  are  shown  in  Fig.  35. 

The  ''Lewis  "  formula*  is: 

W  =  SF  Fy.  (66) 

A  table  indicating  the  value  of  S  for  different  speeds   follows: 

Safe  Working  Stresses  for  Different  Speeds. 

Spood  of  tooth,          100  i       200  ;       300  I       600  i    900  I  1200     1800  i    2400 

ft.  per  mm. 


Castirou        ,     8000!     6000  I     4800  j     4000  i  3003  i  2400  i  2000  :    1700 


Steel  20000  ;  15000  I  12000     10000  i  7500  I  6000     5000      4300 


*XOTE.     A   full   and   convenient   statement   of   the  Lewis   formula   will 
be  found  'in  "Kent 's  Pocket  Book.  " 


134 


MACHINE  DESIGN 


121 


A  usual  relation  of  F  to  P1  is: 


For  cast  teeth,  F  =  2P1  to  3P1. 
For  cut  teeth,  F  =  3P1  to  4P1. 


(66) 
(67) 


The  usual  method  of  handling  these  formulae  is  as  follows: 

The  pitch  circles  of  the  proposed  gears  are  known  or  can  be  assumed; 
hence  W  can  readily  be  figured,  also  the  speed  of  tho  teeth,  whence  S  can 
be  read  from  the  table.  The  desired  relation  of  F  to  P1  can  be  arbitrarily 
chosen,  when  P1  and  y  become  the  only  unknown  quantities  in  the  equation. 
A  shrewd  guess  can  be  made  for  the  number  of  teeth,  and  y  calculated  there- 
from. Then  solve  the  equation  for  PA  which  will  undoubtedly  be  fractional. 
Choose  the  nearest  even  pitch,  or,  if  it  is  desired  to  keep  an  even  diametraj 
pitch,  the  fractional  pitch  that  will  bring  an  even  diametral  pitch.  Now, 
from  this  final  and  corrected  pitch,  and  the  diameter  of  the  pitch  circle, 
calculate  the  number  of  teeth  N  in  the  gear.  Check  the  assumed  value  of  y 
by  this  positive  value  of  N. 

Another  good  way  of  using  this  formula  is  to  start  with  the 
pitch  and  face  desired,  and  the  diameter  of  the  pitch  circle.     In 


Fig.  37. 


this  case  W  is  the  only  unknown  quantity,  and  when  found  can  be 
compared  with  the  load  required  to  be  carried.  If  too  small, 
make  another  and  successive  calculations  until  the  result  approxi- 
mates the  required  load. 

SPUR  GEAR  Rin,  ARHS,  AND  HUB. 

ANALYSIS  and  THEORY.  The  rim  of  a  gear  has  to  transmit 
the  load  on  the  teeth  to  the  arms.  It  is  thus  in  tension  on  one  side 
of  the  teeth  in  action,  and  in  compression  on  the  other.  The  sec- 
tion of  the  rim,  however,  is  so  dependent  on  other  practical  con- 
siderations which  call  for  an  excess  of  strength  in  this  respect,  that 


135 


122 


MACHINE  DESIGN 


it  is  not  considered  worth  \vhile  to  attempt  a  calculation  on  ih\$ 
basis. 

Gears  seldom  run  fast  enough  to  make  necessary  a  calculation 
for  centrifugal  force  ;  and  in  general  it  can  be  said  that  the  design 
of  the  rim  is  entirely  dependent  on  practical  considerations.  These 
will  appear  later  under  k<  Practical  Modification.  " 

The  arms  of  a  gear  are  stressed  the  same  as  pulley  arms,  the 
same  theory  answering  for  both,  except  that  a  gear  rim  always  be- 
ing much  heavier  than  a  pulley  rim,  the  distribution  of  load 
amongst  the  arms  is  better  in  the  case  of  a  gear  than  of  a  pulley, 
and  it  is  usually  safe  to  assume  that  each  arm  of  a  gear  takes  its  full 
proportion  of  load  ;  or.  for  an  oval  section,  equating  the  external 
moment  to  the  internal  moment  as  in  the  case  of  pulleys,  we  have  : 

-^5-  =  0.0393  SA3.  (68) 

Heavy  spur  gears  have  the  arms  of  a  cross  or  T  section  (Fig. 


i 


Fig.  33. 

37i,  the  latter  being  especially  applicable  to  the  case  of  bevel  gears 
where  there  is  considerable  side  thrust.  The  simplest  way  of 
treating  such  sections  is  to  consider  that  the  whole  bending  moment 
is  taken  by  the  rectangular  section  whose  greater  dimension  is  in 
the  direction  of  the  load.  The  rest  of  the  section,  being  close  to 
the  neutral  axis  of  the  section,  is  of  little  value  in  resisting  the 
direct  load,  its  function  being  to  give  sidewise  stiffness.  The 
equation  for  the  cross  or  T  style  of  arm,  then  is  : 


W        I) 

X   ~77~ 


(69) 


136 


MACHINE  DESIGN  123 

Either  b  or  h  may  be  assumed,  and  the  other  determined.  As  a 
guide  to  the  section,  b  may  be  taken  at  about  the  thickness  of  the 
tooth. 

Gear  hubs  are  in  no  wise  different  from  the  hubs  of  pulleys  or 
other  rotating  pieces.  The  depth  necessary  for  providing  suffi- 
cient strength  over  the  key  to  avoid  splitting  is  the  guiding  ele- 
ment, and  can  usually  be  best  determined  by  careful  judgment. 

PRACTICAL  MODIFICATION.  The  practical  requirements, 
which  no  theory  will  satisfy,  are  many  and  varied.  Sudden  and 
severe  shock,  excessive  wear  due  to  an  atmosphere  of  grit  and  corros- 
ive elements,  abrupt  reversal  of  the  mechanism,  the  throwing-in  of 
clutches  and  pawls,  the  action  of  brakes — these  and  many  other 
influences  have  an  important  bearing  on  gear  design,  but  not  one 
that  can  be  calculated.  The  only  method  of  procedure  in  such 
cases  is  to  base  the  design  on  analysis  and  theory  as  previously 
given,  antf  then  add  to  the  face  of  gear,  thickness  of  tooth,  or  pitch 
an  amount  which  judgment  and  experience  dictate  as  sufficient. 

Excessive  noise  and  vibration  are  difficult  to  prevent  at  high 
speeds.  At  1,000  feet  per  minute,  gears  are  apt  to  run  with  an 
unpleasant  amount  of  noise.  At  speeds  beyond  this,  it  is  often 
necessary  to  provide  mortise  teeth,  or  teeth  of  hard  wood  set  into 
a  cast-iron  rim  (see  Fig.  38).  Rawhide  pinions  are  useful  in  this 
regard.  Fine  pitches  with  a  long  face  of  tooth  run  much  more 
smoothly  at  high  speeds  than  a  coarse  pitch  and  narrow-faced  tooth 
of  equal  strength.  Greater  care  in  alignment  of  shafts,  however, 
is  necessary,  also  stiffer  supports. 

Should  it  be  impracticable  to  use  a  standard  tooth  of  sufficient 
strength,  there  are  several  ways  in  .which  we  can  increase  the 
carrying  capacity  without  increasing  the  pitch.  These  are: 

1.  Use  a  stronger  material,  such  as  steel.  „ 

2.  Shroud  the  teeth. 

3.  Use  a  hook  tooth. 

4.  Use  a  stub  tooth. 

Shrouding  a  tooth  consists  in  connecting  the  ends  of  the  teeth 
with  a  rim  of  metal.  When  this  rim  is  extended  to  the  top  of  -the 
tooth,  the  process  is  called  "  full- shrouding"  (Fig.  39);'  and  when 
carried  only  to  the  pitch  line,  it  is  termed  "half-shrouding" 
(Fig.  40).  The  theoretical  effect  of  shrouding  is  to  make  the  tooth 


137 


124 


MACHINE  DESIGN 


act  like  a  short  beam  built  in  at  the  sides;  and  the  tootli  will 
practically  have  to  be  sheared  out  in  order  to  fail.  This  modifica- 
tion of  gear  design  requires  the  teeth  to  be  cast,  as  the  cutter 
cannot  pass  through  the  shrouding.  The  strength  of  the  shrouded 
gear  is  estimated  to  be  from  25  to  50  per  cent  above  that  of  the- 
plain-tooth  type. 


Fig.  39. 


Fig.  40, 


The  hook-tooth  gear  (Fig-  41)  is  applicable  only  to  cases 
where  the  load  on  tho  tooth  does  not  reverse.  The  working  side 
of  the  tooth  is  made  of  the  usual  standard  curve,  while  the  back  is 
made  of  a  curve  of  greater  obliquity,  resulting  in  a  considerable 
increase  of  thickness  at  the  root  of  the  tooth.  A  comparison  of 
strength  between  this  form  and  the  standard  may  be  made  by 
drawing  the  two  teeth  for  a  given  pitch,  measuring  their  thickness 
just  at  top  of  the  fillet,  and  finding  the  relation  of  the  squares 
of  these  dimensions.  The  truth  of  this  relation  is  readily  seen  from 
an  inspection  of  formula  Gl. 

The  stub  tooth  merely  involves  the  shortening  of  the  height 


138 


MACHINE  DESIGK  12o 

of  the  tooth  in  order  to  reduce  the  lever  arm  on  which  the  load 
aqts,  thus  reducing  the  moment,  and  thereby  permitting  a  greater 
load  to  be  carried  for  the  same  stress. 

The  rim  of  a  gear  is  dependent  for  its  proportions  chiefly  on 
questions  of  practical  moulding  and  machining.  It  must  bear  a 
certain  relation  to  the  teeth  and  arms,  so  that,  when  it  is  cooling  in 
the  mould,  serious  shrinkage  stresses  will  not  be  set  up,  forming 
pockets  and  cracks.  Moreover,  when  under  pressure  of  the  cutter 
in  the  producing  of  the  teeth,  it  must  not  chatter  or  spring.  This 
condition  is  quite  well  attained  in  ordinary  gears  when  the  thick- 
ness of  the  rim  below  the  base  of  the  tooth  is  made  about  the  same 
as  the  thickness  of  the  tooth. 


LIGHT   PRESSURE 
ON  BACK  OF  TOOTH. 
35ell> 


LOADED  SIDE 
5"  INVOLUTE. 


Fig.  41. 

The  stiffening  ribs  and  arms  must  all  be  joined  to  the  rim  by 
ample  fillets,  and  the  cross-section  must  be  as  uniform  as  possible, 
to  prevent  unequal  cooling  and  consequent  pulling-away  of  the 
arms  from  the  rim  or  hub.  Often  the  calculated  size  of  the  arms 
at  both  rim  and  hub  has  to  be  modified  considerably  to  meet  this 
requirement. 

The  arms  are  usually  tapered  to  suit  the  designer's  eye,  a 
small  gear  requiring  more  taper  per  foot  than  a  large  one.  Both 
rim  and  hub  should  be  tapered  ^  inch  per  foot  to  permit  easy 
drawing-out  from  the  mould. 

The  proportions  given  in  the  following  table  have  been  used 
with  success  as  a  basis  of  gear  design  in  manufacturing  practice. 
The  table  will  serve  as  an  excellent  guide  in  laying  out,  and  can  be 
closely  followed,  in  most  cases  with  but  slight  modification. 
Web  gears  are  introduced  for  small  diameters  where  the  arms  begin 
to  look  awkward  and  clumsy. 


139 


120 


MACHINE  DESIGN 


Gear  Design  Data. 

Measurements  given  in  inches.    Letters  refer  to  Fig.  42 


Diametral  pitch  .  . 

P 

1* 

« 

2 

2i 

3 

Si 

4 

5 

6 

8 

Face 

F 

51 

3| 

3V 

2| 

91 

91 

I? 

U 

d 

a 

Thickness   of  arm 
\v  h  e  n  extended 
to  pitch  line.  .  .  . 

G 

If 

u 

1 

7 

•u 

s, 

H 

JS 

8 

A 

Width  of  arm  when 
extended     to 
pitch  line  

c 

4 

^ 

3 

2J 

2J 

2 

li 

1A 

I3 

Thickness  of  rim  .  . 

K 

2| 

2| 

2J 

11 

H 

If 

H 

1 

3 

1 

Depth  of  rib  

E 

2 

It 

H 

H 

1 

1 

5 

1 

i 

8 

Thickness  of  web. 

T 

H 

1 

8 

1 

s 

9 

1  (J 

4 

A 

8 

"1  0 

Number  of  arms,  6. 

Give  inside  of  rims  and  hub  a  draft  of  i  inch  per  foot. 

BEVEL  GEARS. 

NOTATION  -The  following  notation  is  used  throughout  the  chapter  on  Bevel  Gears : 

A  =  Apex  distance  at  pitch  element  of 

cone  (inches). 
A'  =  Apex    distance   at  bottom    element 

of  tooth  (inches). 

]>  =  Angle  of  bottom  of  tooth  (degrees). 
C  =  Pitch  angle  (degrees). 
D  = Pitch  diameter  (inches). 
E  =  Radius  increment  of  gear  (inches). 
F  =Face  of  gear  (inches). 
/    ^Clearance  at  bottom  (inches). 
O   =  Angle  of  face  (degrees). 
H  =Cutting  angle  (degrees). 
K  =Radius       increment        of      pinion 

(inches). 

N  =  Number  of  teeth. 
I^1— Formative     number     of    teeth,    or 

the  number  corresponding  to  the 

spur  gear  on  which  the  outline  of 

toot  h  is  made. 

ANALYSIS.      It  is   possible  to   consider  bevel  gears  as  the 
general   case  of  which  spur  gears  are  a  special  form.     The  pitch 


O  D=Outside  diameter  (inches). 

P      =Diamctral  pitch  related  to  pitch 

diameter  (teeth  per  inch). 
Pi     =Circular  pitch    measured  on   the 

circumference  of  D  (inches). 
S      =  Working  strength  of  material  (Ibs. 

per  sq.  in.). 
s        =Addendum,    or    height    of    tooth 

above  pitch  line  (inches). 
«+/=  Depth  of  tooth  below  pitch  line 

(inches). 

T      =Anglo  of  top  of  tooth  (degrees). 
t        =Thickness  of  tooth   at  pitch  line 

(inches). 

W    =  Working  load  at  pitch  line  (Ibs.). 
y       =Factor  in  "Lewis"  formula. 


140 


MACHINE  DESIGN 


127 


surfaces  of  spur  gears  described  above  as  cylinders,  mathematically 
considered,  are  cones  whose  vertices  are  infinitely  distant,  while 
bevel  gears  likewise  are  based  on  pitch  cones,  but  with  a  vertex  at 
some  finite  point,  common  to  the  mating  pair.  Hence,  as  we 
might  expect,  the  laws  of  tooth  action  are  similar  in  bevel  gears 
to  those  in  the  case  of  spur  gears.  The  profile  of  the  tooth  in  the 
former  case,  however,  is  based,  not  on  the  real  radius  of  the  pitch 
cone,  but  on  the  radius  of  the  normal  cone  ;  and  in  the  develop- 
ment of  the  outline  the  latter  is  treated  just  as  though  it  were  the 
radius  of  a  spur  gear.  The  tooth  thus  formed  is  wrapped  back  up- 
on the  normal  cone  face,  and  becomes  the  large  end  of  the  taper- 
ing bevel-gear  tooth  (see  Fig.  44). 


Fig.  42. 

The  teeth  of  bevel  gears,  being  simply  projections  with  bases  on 
the  pitch  cones,  have  a  varying  cross-section  decreasing  toward  the 
vertex  ;  also  a  trapezoidal  section  of  root,  the  latter  section  acting 
as  a  beam  section  to  resist  the  cantilever  moment  due  to  the  tooth 
load. 

The  arms  inust,  as  in  the  case  of  spur  gears,  transmit  the  load 
from  the  tooth  to  the  shaft;  in  addition,  the  arms  of  a  bevel  gear 
are  subjected  to  a  side  thrust  due  to  the  wedging  action  of  the 
cones.  Hence  sidewise  stiffness  of  the  arms  is  more  essential  in 
this  type  of  gear  than  in  the  case  of  the  spur  gear. 

THEORY.  It  is  evident  that  the  calculation  of  tooth  strength 
based  on  a  trapezoidal  section  of  root  would  be  somewhat  compli- 


141 


128 


MACHINE  DESIGN 


cated  ;  also  that  the  trapezoid  in  most  cases  would  be  but  little 
different  from  a  true  rectangle.  Hence  the  error  will  be  but 
slight  if  the  average  cross-section  of  the  tooth  be  taken  to  repre- 
sent its  strength,  and  the  calculation  made  accordingly. 


142 


130 


MACHINE  DESIGN 


Fitr.  45  shows  a  bevel-gear  tooth  with  the  averao-e  cross-sec- 
tion in  dotted  lines.  For  the  purpose  of  calculation,  the  assump- 
tion is  made  that  the  section  A  is  carried  the  full  length  of  the 
face  of  the  gear,  and  that  the  load  which  this  average  tooth  must 
carry  is  the  calculated  load  at  the  pitch  line  of  section  A.  This 
is  equivalent  to  saying  that  the  strength  of  a  bevel-gear  tooth  is 
equal  to  that  of  a  spur-gear  tooth  which  has  the  same  face,  and  a 
section  identical  with  that  cut  out  by  a  plane  at  the  middle  of  the 
bevel  tooth.  The  load,  as  in  the  case  of  the  spur  gear,  should  be 
taken  at  the  top  of  the  tooth;  and  its  magnitude  can  be  con- 
veniently calculated  at  tlie  mean  pitch  radius  of  the  bevel  face, 
without  appreciable  error. 

This  similarity  to  spur  gears  being  borne 
in  mind,  the  calculation  for  strength  needs  no 
further  treatment.  Once  the  average  tooth  is 
assumed  or  found  by  layout,  a  strict  following- 
out  of  the  methods  pursued  for  spur-gear 
teeth  will  bring  consistent  results. 

The  detail  design  of  a  pair  of  bevel  gears 
involves  some  trigonometrical  computations 
in  order  properly  to  dimension  the  drawing 
for  use  in  finishing  the  blanks  and  subse- 
quently in  cutting  the  teeth,  or.  in  the  case 
of  cast  gears,  in  making  the  pattern.  These 

calculations,  although  simple,  are  yet  apt  to  be  tedious;  and  inac- 
curacies are  likely  to  creep  in  if  a  definite  system  of  relations 
be-  not  maintained.  Hence  the  results  of  these  calculations  are 
given  below  in  condensed  and  reduced  form.  The  deduction  of 
these  formulae  is  a  simple  and  interestincr  exercise  in  trigonometry; 
and  it  is  urged  that  they  be  worked  out  by  the  student  from  the 
figure,  in  which  case  he  will  feel  greater  confidence  in  their  use. 


Axes  of  Gears  at  90  Degrees. 

Use  subscript  1  for  gear;  P  for  pinion.     Letters  refer  to  Fig.  44. 

p-2L_    ? 

-  ]>    -    pi' 

1  P' 

-  p    ~     77  ' 

P'  7T 


(70) 
(71) 
(72) 


144 


MACHINE  DESIGN  131 


t            P1           TT 

f  -  10  ~  20  ~  20P' 
tan  Cp  =  j^-;  tan  Ci  =  ^-- 

(73) 
(74) 

tanT   =-£=        N 

(75) 

tan  B  =  jL+/  =  2.31^sm  C 

(76) 

s  +/  =  A  tan  B  =  ^^  =  (X3G8F'. 
N               1                                   1 

(77) 

A  =  2P  sin  C  =  2P  1/Nl2  +  NP2  =  ~2~  I7  I>i2  - 

f  DP2.    (78) 
(79) 

(80) 
(81) 
(82) 

A       cos  B       2P  cos  B  sin  C     ' 
Gi  =  90°  -  (Ci  +  T  )  ;  GP  =  90°  -  (Cp  +  T). 
E  =  S  cos  Ci  =  S  sin  CP  . 
K  =  S  cos  Cp  =  S  sin  Ci. 

PRACTICAL  MODIFICATION.  The  practical  requirements 
to  be  met  in  transmission  of  power  by  bevel  gears  are  the  same  as 
for  spur  gears;  but  in  the  case  of  bevel  gears  even  greater  care  is 
necessary  to  provide  stiffness,  strength,  true  alignment,  and  rigid 
supports.  As  far  as  the  gears  themselves  are  concerned,  a  long 
face  is  desirable;  but  it  is  much  more  difficult  to  gain  the  ad- 
vantage of  its  strength  than  in  the  case  of  spur  gears,  because  full 
bearing  along  the  length  of  the  tooth  is  hard  to  guarantee. 

The  rim  usually  requires  a  series  of  ribs  running  to  the  hub 
to  give  required  stiffness  and  strength  against  the  side  thrust  which 
is  always  present  in  a  pair  of  bevel  gears.  Instead  of  arms,  the 
tendency  of  bevel -gear  design,  except  for  very  large  gears,  is  toward 
a  web  on  .  account  of  the  bette^  and  more  uniform  connection 
thereby  secured  between  rim  and  hub.  This  web  may  be  lightened 
by  a  number  of  holes,  so  that  the  resultant  effect  is  that  of  a  num- 
ber of  wide  and  flat  arms. 

The  hubs  naturally  have  to  be  fully  as  long  as  those  of  spur 
gears,  because  there  is  greater  tendency  to  rock  on  the  shaft,  due 
to  the  side  thrust  from  the  teeth,  mentioned  above. 

The  teeth  on  small  gears  are  cut  with  rotary  cutters,  at  least 
two  finishing  cuts  being  necessary,  one  for  each  side  of  the  taper- 
ing tooth.  The  more  accurate  method  is  to  plane  the  teeth  on  a 
special  gear  planer,  and  this  method  is  followed  on  all  gears  of 
any  considerable  size.  The  practical  requirement  here  is  that  no 
portion  of  the  hub  shall  project  so  as  to  interfere  with  the  stroke 


145 


i:!2  MACHINE  DESIGN 

of  the  planer  tool.  The  requirements  of  gear  planers  vary  some- 
what in  this  regard. 

Finally,  after  all  that  is  possible  has  been  done  in  the  design 
of  the  gear  itself  to  render  it  suitable  to  withstand  the  varied 
stresses,  especial  attention  must  be  paid  to  the  rigidity  of  the 
supporting  shafts  and  bearings.  Bearings  should  always  be  close 
up  to  the  hubs  of  the  gears,  and,  if  possible  the  bearing  for  both 
pinion  and  gear  should  be  cast  in  the  same  piece.  If  this  is  not 
done,  the  tendency  of  the  separate  bearings  to  get  out  of  line  and 
destroy  the  full  bearing  of  the  teeth  is  difficult  to  control.  Thrust 
washers  are  desirable  against  the  hubs  of  both  pinion  and  gear; 
also  proper  means  of  well  lubricating  the  same. 

"With  these  considerations  carefully  met,  bevel  gears  are  not 
the  bugbear  of  machine  design  that  they  are  sometimes  claimed 
to  be.  The  common  reason  why  bevel  gears  cut  and  fail  to  work 
smoothly,  is  that  the  gears  and  supports  are  not  designed  carefully 
enough  in  relation  to  each  other.  This  is  also  true  of  spur  gears, 
but  the  bevel  gear  will  reveal  imperfections  in  its  design  far  the 
more  quickly  of  the  two. 

WORM  AND  WORM  GEAR. 

NOTATION— The  following  notation  is  used  throughout  the  chapter  on  Worm  and 
W^rni  Gear: 

I)    —Pitch  diameter  of  gear  (inches).  IJ1  =Circular     pitch  =  Pitch     (if    worm 

K   =  Efficiency  between  worm  shaft  and  thread  (inches). 

gear  shaft  (per  cent).  R    =  Radius  of  pitch  circle  of  worm  gear 

f     =Clearauce     of     tooth     at     bottom  .^               (inches). 

(inches).  s     =  Addendum  of  tooth  (inches). 

/      =  Index  of  worm  thread  (1  for  single'  T    =  Twisting    moment    on    gear    shaft 

2  for  double,  etc.).  (inch-lbs.). 

}j    =  Load  of  worm  thread  (inches).  Txv=T\visting   moment  qn  worm    shaft 

M    =  Revolutions    of     gear     shaft     per  (inch-lbs.). 

minute.  t     =  Thickness   of  to'oth    at    pitch    line 

Mw  =  Revolutions    of    worm    shaft     per  (inches). 

minute.  W  =Load  at  pitch  line  (Ibs.). 
X    =  Number  of  teeth  i:i  gear. 

ANALYSIS.  The  simplest  way  of  analyzing  the  case  of  the 
worm  and  worm  gear  is  to  base  it  upon  an  ordinary  screw 
and  nut.  Take,  for  example,  the  lead  screw  of  a  common  lathe. 
The  carriage  carries  a  nut,  through  which  the  lead  screw  passes. 
BV  the  rotation  of  the  screw,  the  carriage,  being  constrained  by  the 
guides  to  travel  lengthwise  of  the  ways,  is  moved.  This  motion 


143 


MACHINE  DESIGN  133 


is,  for  a  single -threaded  screw,  a  distance  per  revolution  equal  to 
the  lead  of  the  screw. 

Now,  suppose  that  the  carriage,  instead  of  sliding  along  the 
ways,  is  compelled  to  turn  about  an  axis  at  some  point  below  the 
ways.  Also,  suppose  the  top  of  the  nut  to  be  cut  off,  and  its  length 
made  endless  by  wrapping  it  around  a  circle  struck  from  the  center 
about  which  the  carriage  rotates.  This  reduces  the  nut  to  a 
peculiar  kind  of  spur  gear,  the  partial  threads  of  the  nut  now 
having  the  appearance  of  twisted  teeth. 

This  special  form  of  spur  gear,  based  on  tne  idea  of  a  threaded 
nut,  is  known  as  a  worm  gear,  and  the  screw  is  termed  a  worm. 
The  teeth  are  loaded  similarly  to  those  of  a  spur  gear,  but  with  the 
additional  feature  of  a  large  amount  of  sliding  along  the  tooth 
surfaces.  This,  of  course,  means  considerable  friction;  and  it  is  in 
fact  possible  to  utilize  the  worm  and  worm  gear  as  an  efficient 
device,  only  by  running  the  teeth  constantly  in  a  bath  of  oil. 
Even  then  the  pressures  have  to  be  kept  well  down  to  insure  the 
required  term  of  life  of  the  tooth  surfaces. 

It  is  evident  that  for  one  revolution  of  a  single-threaded  worm, 
one  tooth  of  the  gear  will  be  passed.  The  speed  ratio  between  the 
worm  gear  and  worm  shaft  will  then  be  equal  to  the  number  of 
teeth  in  the  gear,  which  is  relatively  great.  Hence  the  worm  and 
worm  gear  are  principally  useful  in  giving  large  speed  reduction 
in  a  small  amount  of  space. 

THEORY.  The  theory  of  worm-wheel  teeth  is  complicated 
and  obscure.  The  production  of  the  teeth  is  simple,  a  dummy  worm 
with  cutting  edges,  called  a  "hob,"  being  allowed  to  carve  its  way 
into  the  worm-gear  blank,  thus  producing  the  teeth  and  at  the 
same  time  driving  the  worm  gear  about  its  axis. 

It  is  clear  that  if  we  know  the  torsional  moment  on  the  worm- 
gear  shaft,  and  the  pitch  radius  of  the  worm  gear,  we  can  find  the 
load  on  the  teeth  at  the  pitch  line  by  dividing  the  former  by  the 
latter.  Expressed  as  an  equation: 

WR  =  T;orW=^-.  (83) 

How  we  shall  consider  this  value  of  W  as  distributed  on  the 
teeth,  is  a  question  difficult  to  answer.  The  teeth  not  only  are 


147 


184  MACHINE  DESIGN 

Curved  to  embrace  the  worm,  but  are  twisted  across  the  face  of  the 
gear,  so  that  it  would  be  practically  impossible  to  devise  a  purely 
theoretical  method  of  exact  calculation.  The  most  reasonable  thing 
to  do  is  to  assume  the  teeth  as  being  equally  as  strong  as  spur-gear 
teeth  of  the  same  circular  pitch,  and  to  figure  them  accordingly. 
It  is  probably  true,  however,  that  the  load  is  carried  by  more  than 
one  tooth,  especially  in  a  hobbed  wheel;  so  we  shall  be  safe  in 
assuming  that  two — and,  in  case  of  large  wheels,  three — teeth 
divide  the  load  between  them.  "With  these  considerations  borne 
in  mind,  the  case  reduces  itself  to  that  of  a  simple  spur-gear 
tooth  calculation,  which  has  already  been  explained  under  the 
heading  "Spur  Gears." 

The  worm  teeth,  or  threads,  are  probably  always  stronger  than 
the  worm-gear  teeth;  so  no  calculation  for  their  strength  need  be 
made. 

The  twisting  moment  on  the  worm  shaft  is  not  determined  so 
directly  as  in  the  case  of  spur  gears.  The  relative  number  of 
revolutions  of  the  two  shafts  depends  upon  the  "  lead "  of  the 
worm  thread  and  the  number  of  teeth  in  the  gear. 

Lead  ( L )  is  the  distance  parallel  to  the  axis  of  the  worm  which 
any  point  in  the  thread  advances  in  one  revolution  of  the  worm. 
Pitch  (P1)  is  the  distance  parallel  to  the  axis  of  the  worm  between 
corresponding  points  on  adjacent  threads.  The  distinction  between 
lead  and  pitch  should  be  carefully  observed,  as  the  two  are  often 
confounded,  one  with  the  other. 

The  thread  may  be  single,  double,  triple,  etc.,  the  index  of  the 
thread  /',  being  1,  2,  3,  etc.,  in  accordance  therewith.  The  relation 
between  lead  and  pitch  may  then  be  expressed  by  an  equation,  thus: 

L  =  I  P.  (84) 

"When  the  index  of  the  thread  is  changed  the  speed  ratio  is 
changed,  the  relation  being  shown  by  the  equation: 

£-»•  <*«> 

If  the  efficiency  were  100  per  cent-  between  the  two  shafts, 
the  twisting  moments  would  be  inversely  as  the  ratio  of  the  speeds 
thus: 


148 


MACHINE  DESIGN  135 


M 


Tw  =       ;  (86) 

but  for  an  efficiency  E  the  equation  would  be: 
T  i 


T- 


The  diameter  of  the  worm  is  arbitrary.  Change  of  thie 
diameter  has  no  effect  on  the  speed  ratio.  It  has  a  slight  effect  OL 
the  efficiency,  the  smaller  worm  giving  a  little  higher  efficiency. 
The  diameter  of  the  worm  runs  ordinarily  from  3  to  10  times  the 
circular  pitch,  an  average  value  being  4P1  or  5P1. 

A  longitudinal  cross-section  through  the  axis  of  the  worm 
cuts  out  a  rack  tooth,  and  this  tooth  section  is  usually  made  of  the 
standard  14^°  involute  form  shown  in  Fig.  46  for  a  rack. 

The  end  thrust,  of  a  mag- 
nitude practically  equal  to  the 
pressure  between  the  teeth, 
has  to  be  taken  by  the  hub  of 
the  worm  against  the  face  of 
'the  shaft  bearing.  A  serious 
loss  of  efficiency  from  friction  Fig.  46. 

is  likely  to  occur  here.     This 

is  often  reduced,  however,  by  roller  or  ball  bearings.  With  two 
worms  on  the  same  shaft,  each  driving  into  a  separate  worm  gear, 
it  is  possible  to  make  one  of  the  worms  right-hand  thread,  and 
the  other  left-hand,  in  which  case  the  thrust  is  self-contained  in 
the  shaft  itself,  and  there  is  absolutely  no  end  thrust  against  the 
face  of  the  bearing.  This  involves  a  double  outfit  throughout,  and 
is  not  always  practicable. 

There  are  few  mathematical  equations  necessary  for  the  dimen- 
sioning of  a  worm  and  worm  gear.  The  formulae  for  the  tooth 
parts  as  given  on  page  120  apply  equally  well  in  this  case. 

PRACTICAL  MODIFICATION.  The  discussion  of  the  effi- 
ciency E  of  the  worm  and  worm  gear  is  more  of  a  practical  than 


149 


130  MACHINE  DESIGN 


of  a  theoretical  nature.  It  seems  to  be  true  from  actual  operation, 
as  well  as  theory,  that  the  steeper  the  threads  the  higher  the  effi- 
ciency. In  actual  practice  we  seldom  have  opportunity  to  change 
the  slope  of  the  thread  to  get  increased  efficiency.  The  slope 
is  usually  settled  from  considerations  of  speed  ratio,  or  available 
space,  or  some  other  condition.  The  usual  practical  problem  is  to 
take  a  given  worm  and  worm  gear,  and  to  make  out  of  it  as  efficient 
a  device  as  possible.  With  hobbed  gears  running  in  oil  baths,  and 
with  moderate  pressures  and  speeds,  the  efficiency  will  range  between 
40  per  cent  and  70  per  cent.  The  latter  figure  is  higher  than  is 
usually  attained. 

To  avoid  cutting  and  to  secure  high  efficiency,  it  seems  es- 
sential to  make  the  worm  and  the  gear  of  different  materials. 
The  worm-thread  surfaces  being  in  contact  a  greater  number  of 
times  than  the  gear  teeth,  should  evidently  be  of  the  harder  material. 
Hence  we  usually  find  the  worm  of  steel,  and  the  gear  of  cast  iron, 
brass,  or  bronze.  To  save  the  expense  of  a  large  and  heavy  bronze 
gear,  it  is  common  to  make  a  cast-iron  center  and  bolt  a  bronze 
rim  to  it. 

The  worm,  being  the  most  liable  to  replacement  from  wear, 
it  is  desirable  so  to  arrange  its  shaft  fastening  and  general  acces- 
sibility that  it  may  be  readily  removed  without  disturbing  the 
worm  gear. 

The  circular  pitch  of  the  gear  and  the  pitch  of  the  worm 
thread  must  be  the  same,  and  the  practical  question  comes  in  as  to 
the  threads  per  inch  possible  to  be  cut  in  the  lathe  in  the  pro- 
duction of  the  worm  thread.  The  pitch  must  satisfy  this  require- 
ment; hence  the  pitch  will  usually  be  fractional,  and  the  diameter 
of  the  worm  gear,  to  give  the  necessary  number  of  teeth,  must  be 
brought  to  it.  While  it  would  perhaps  be  desirable  to  keep  an 
even  diametral  pitch  for  the  worm  gear,  yet  it  would  be  poor  de- 
sign to  specify  a  worm  thread  which  could  not  be  cut  in  a  lathe. 

The  standard  involute  of  1-44°,  and  the  standard  proportions 
of  teeth  as  given  on  page  120  are  usually  used  for  worm  threads. 
This  system  requires  the  gear  to  have  at  least  30  teeth,  for  if  fewer 
teeth  are  used  the  thread  of  the  worm  will  interfere  with  the 
flanks  of  the  gear  teeth.  This  is  a  mathematical  relation,  and 
there  are  methods  of  preventing  it  by  change  of  tooth  proportions 


150 


MACHINE  DESIGN  137 

» 

or  of  angle  of  worm  thread  ;  but  there  are  few  instances  in  which 
less  than  30  teeth  are  required,  and  it  is  not  deemed  worth  while 
to  go  into  a  lengthy  discussion  of  this  point. 

The  angle  of  the  worm  embraced  by  the  worm-gear  teeth 
varies  from  60°  to  90°,  and  the  general  dimensions  of  rim  are  made 
about  the  same  as  for  spur  gears.  The  arms,  or  the  web,  have  the 
same  reasons  for  their  size  and  shape.  Probably  web  gears  and 
cross-shaped  arms  are  more  common  than  oval  or  elliptical  sections. 

Worm  gears  sometimes  have  cast  teeth,  but  they  are  for  the 
roughest  service  only,  and  give  but  a  point  bearing  at  the  middle 
of  the  tooth.  An  accurately  hobbed  worm  gear  will  give  a  bearing 
clear  across  the  face  of  the  tooth,  and,  if  properly  set  up  and  cared 
for,  makes  a  good  mechanical  device  although  admittedly  of  some- 
what low  efficiency. 

Fig.  47  shows  a  detail  drawing  of  a  standard  worm  and  worm 
gear.  It  should  serve  as  a  suggestion  in  design,  and  an  illustration 
of  the  shop  dimensions  required  for  its  production. 

PROBLEMS  ON  SPUR,    BEVEL,  AND   WORM   GEARS. 

1.  Calculate  proportions    of    a    standard    Brown  &  Sharpe 
gear  tooth  of  1^  diametral  pitch,   making  a  rough  sketch  and  put- 
ting the  dimensions  on  it. 

2.  Suppose  the  above  tooth  to  be  loaded  at  the    top  with 
5,000  Ibs.     If  the  face  be  6  inches,  calculate  the  fiber  stress  at  the 
pitch  line,  due  to  bending. 

3.  A  tooth  load  of  1,200  Ibs.  is  transmitted  between  two 
spur  gears  of  12-inch  and  30-inch  diameter,  the  latter  gear  making 
100  revolutions  per  minute.     Calculate  a  suitable  pitch  and  face 
of  tooth  by  the  "  Lewis  "  formula. 

4.  Assuming  a  ^-inch  web  on  the  12-inch  gear,  calculate  the 
shearing  fiber  stress  at  the  outside  of  a  hub  4  inches  in  diameter 

5.  Design  elliptical  arms    for    the    30-inch  gear,    allowing 
S  =  2,200. 

6.  Design  cross-shaped  arms  for  30-inch  gear. 

7.  Calculate  the  dimensions  shown   in  formulae  70  to  82  in- 
clusive for  a  pair  of  bevel  gears  of  20  and  60  teeth  respectively,  2 
diametral  pitch,  and  4-inch  face.     (The  use   of  logarithmic  tables 
makes  the  calculation  much  easier  than  with  the  natural  functions.) 


151 


MACHINE  DESIGN 


139 


8.     A  worm  wheel  has  40  teeth,  3  diametral  pitch,  and  double 
thread.     Calculate  (#)  its  lead;  (£)  its  pitch  diameter. 

FRICTION  CLUTCHES. 

DOTATION— The  following  notation  is  used  throughout  the  chapter  on  Friction  Clutches : . 

a  =  Angle  between  clutch  face 
and  axis  of  shaft  (degrees) 

H  =Horse-power  (33jOOO  ft.-lbs. 
per  minute). 

]JL  =  Coefficient  of  friction  (per 
cent). 

N  ^Number  of  revolutions  per 
minute. 

P  = Force  to  hold  clutch  in  gear 
to  produce  W  (Ibs.). 

R  =Mean  radius  of  friction  sur- 
face (inches). 

T  =Twisting  moment  about 
shaft  axis  (inch-lbs.). 

V  = Force  normal  to  clutch  face 
(Ibs.). 

W=Load  at  mean  radius  of 
friction  surface  (Ibs.). 

ANALYSIS.       The 

friction  clutch  is  a  de- 
vice for  connecting  at 
oo  will  two  separate  pieces 
of  shaft,  transmitting  an 
amount  of  power  be- 
tween them  to  the  capac- 
ity of  the  clutch.  The 
connection  is  usually  ac- 
complished while  the 
driving  shaft  is  under 
full  speed,  the  slipping 
bet  /een  the  surfaces 
which  occurs  during  the 
throwing-in  of  the 
clutch,  permitting  the 
driven  shaft  to  pick  up 
the  speed  of  the  other 
gradually,  without  ap- 
preciable shock.  The 
disconnection  is  made  in 
the  same  manner,  the 


153 


140 


MACHINE  DESIGN 


amount  of  slipping  which  occurs  depending  on  the  suddenness  with 
which  the  clutch  is  thrown  out. 

The   force  of  friction  is  the  sole  driving  element,  hence  the 

problem  is  to  secure  as 
large  a  force  of  friction 
as  possible.  But  friction 
cannot  be  secured  with- 
out a  heavy  normal  pres- 
sure between  surfaces 
having  a  high  coefficient 
of  friction  between  them. 
The  many  varieties  of 
friction  clutches  which 
are  on  the  market  or  de- 
signed for  some  special 
purpose,  are  all  devices 
for  accomplishing  one 
and  the  same  effect,  vis., 
the  production  of  a  heavy 
normal  force  or  pressure 
between  surfaces  at  such 
a  radius  from  the  driven 
axis,  that  the  product  of 
the  force  of  friction 
thereby  created  and  the 
radius  shall  equal  the 
desired  twisting  moment 
about  that  axis. 

Three  typical  meth- 
odsof  accomplishing  this 
are  shown  in   Figs.  48, 
49,    and   50.      None  of 
these  drawings  is  worked 
out  in  operative   detail. 
They  are    merely    illus- 
trations of  principle,  and  are  drawn  in  the  simplest  form  for  that 
purpose. 

In  Eig.  48  the  normal  pressure  is  created  in  the  simplest  pos- 


154 


MACHINE  DESIGN 


141 


sible  way,  an  absolutely  direct  push  being  exerted  between  the 
discs,  due  to  the  thrust  P  of  the  clutch  fork. 

In  Fig.  49  advantage  is  taken  of  the  wedge  action  of  the  in- 
clined faces,  the  result  be- 
ing that  it  takes  less  thrust 
P  to  produce  the  required 
normal  pressure  at  the  ra- 
dius II. 

In  Fig.  50  the  inclin- 
ation of  the  faces  is  carried 
so  far  that  the  angle  a  of 
Fig.  49  has  become  zero; 
and  by  the  toggle-joint  ac- 
tion of  the  link  pivoted  to 
the  clutch  collar,  the  nor- 
mal force  produced  may  .be 
very  great  for  a  slight  thrust 
P.  By  careful  adjustment 
of  the  length  of  the  link  so 
that  the  jaw.  takes  hold  of 
the  clutch  surface,  when 
the  link  stands  nearly  ver- 
tical, a  very  easy  operating 
device  is  secured,  and  the 
thrust  P  is  made  a  mini- 
mum. 

THEORY.  Referring 
to  Fig.  48  in  order  to  cal- 
culate the  twisting  mo- 
ment, we  must  remember 
that  the  force  of  friction 
between  two  surfaces  is 
equal  to  the  normal  pres- 
sure times  the  coefficient  of 
friction.  This,  in  the  form 
of  an  equation,  using  the  symbols  of  the  figure,  is  : 

W  =  p  P.  (88) 


155 


142  MACHINE  DESIGN 

Hence  we  may  consider  that  we  have  a  force  of  magnitude  ftP 
acting  at  the  mean  radius  II  of  the  clutch  surface.  The  twisting 
moment  will  then  be  : 

T  =  AVR  =  /xPR.  (89) 

Referring  to  equation  54,  which  gives  twisting  moment  in  terms 
of  horse-power,  and  putting  the  two  expressions  equal  to  each  other, 
we  have  : 


This  expression  gives  at  once  the  horse-power  that  the  clutch  will 
transmit  with  a  given  end  thrust  P. 

In  Fig.  49  the  equilibrium  of  the  forces  is  shown  in  the  little 
sketch  at  the  left  of  the  figure.  The  clutch  faces  are  supposed 
to  be  in  gear,  and  the  extra  force  necessary  to  slide  the  two  to- 
gether is  not  considered,  as  it  is  of  small  importance.  The  static 
equations  then  are  : 

P  =  2  —  sin  a  ; 

or,  Y  —  P  cosec  a.  (90 

TV  =  /jiV      =    pP  cosec  a.  (92) 

T  =  TVR  =  ^PR  cosec  a.  (93) 


H  =  (94) 


In  Fig.  50,  P  would  of  course  be  variable,  depending  on  the 
inclination  of  the  little  link.  The  amount  of  horse-power  which 
this  clutch  would  transmit  would  be  the  same  as  in  the  case  of  the 
device  illustrated  in  Fig.  49,  for  an  equal  normal  force  Y  produced. 

The  further  theoretical  design   of  such  clutches  should  be  in 

O 

accordance  with    the  same   principles  as    for  arms    and  webs   of 
pulleys,  gears,  etc.     The  length  of  the  hubs  must  be  liberal  in 


156 


MACHINE  DESIGK  U3 

order  to  prevent  tipping  on  tlie  shaft  as  a  result  of  uneven  wear. 
The  end  thrust  is  apt  to  be  considerable;  and  extra  side  stiffness 
must  be  provided,  as  well  as  a  rim  that  will  not  spring  under  the 
radial  pressure. 

PRACTICAL  HODIFICATION.  It  is  desirable  to  make  the 
most  complicated  part  of  a  friction  clutch  the  driven  part,  for  then 
the  mechanism  requiring  the  closest  attention  and  adjustment  may 
be  brought  to  and  kept  at  rest  when  no  transmission  of  power  is 
desired. 

Simplicity  is  an  important  practical  requirement  in  clutches. 
The  wearing,  surfaces  are  subjected  to  severe  usage;  and  it  is 
essential  that  they  be  made  not  only  strong  in  the  first  place,  but 
also  capable  of  being  readily  replaced  when  worn  out,  as  they  are 
sure  to  be  after  some  service. 

The  form  of  clutch  shown  in  Fig.  50  is  the  most  efficient 
form  of  the  three  shown,  although  its  commercial  design  is  consid- 
erably different  from  that  indicated.  Usually  the  jaws  grip  both 
sides  of  the  rim,  pinching  it  between  them.  This  relieves  the 
clutch  rim  of  the  radial  unbalanced  thrust. 

Adjusting  screws  must  be  provided  for  taking  up  the  wear, 
and  lock  nuts  for  maintaining  their  position. 

Theoretically,  the  rubbing  surfaces  should  be  of  those  materials 
whose  coefficient  of  friction  is  the  highest;  but  the  practical  ques- 
tion of  wear  comes  in,  and  hence  we  usually  find  both  surfaces  of 
metal,  cast  iron  being  most  common.  For  metal  on  metal  the 
coefficient  of  friction  JJL  cannot  be  safely  assumed  at  more  than  15 
per  cent,  because  the  surfaces  are  sure  to  get  oily. 

A  leather  facing  on  one  of  the  surfaces  gives  good  results  as 
to  coefficient  of  friction,  p.  having  a  value,  even  for  oily  leather,  of 
20  per  cent.  Much  slipping,  however,  is  apt  to  burn  the  leather; 
and  this  is  most  likely  to  occur  at  high  speeds. 

Wood  on  cast  iron  gives  a  little  higher  coefficient  of  friction 
for  an  oily  surface  than  metal  on  metal.  Wood  blocks  can  be  so 
set  into  the  face  of  the  jaws  as  to  be  readily  replaced  when  worn, 
and  in  such  case  make  an  excellent  facing. 

The  angle  a  of  a  cone  friction  clutch  of  the  type  shown  in 
Fig.  49,  may  evidently  be  made  so  small  that  the  two  parts  will 
wedge  together  tightly  with  a  very  slight  pressure  P;  or  it  may 


157 


144 


MACHINE  DESIGN 


158 


MACHINE  DESIGN  145 


be  so  large  as  to  have  little  wedging  action,  and  approach  the  con- 
dition illustrated  in  Fig.  48.  Between  these  limits  there  is  a 
practical  value  which  neither  gives  a  wedging  action  so  great  as  to 
make  the  surfaces  difficult  to  pull  apart,  nor,  on  the  other  hand, 
requires  an  objectionable  end  thrust  along  the  shaft  in  order  to 
make  the  clutch  drive  properly. 

For  a  =  about  15°,  the  surfaces  will  free  themselves  whenP  is  relieved. 
"    a  =       "       12°,    "         "         require  slight  pull  to  be  freed. 
"    a  =       "       10°,    "         "         cannot  be  freed  by  direct  pull  of  the 
hand,  but  require  some  leverage  to  produce  the  necessary  force  P. 

PROBLEMS  ON  FRICTION   CLUTCHES. 

1.  With  what  force  must  we  hold   a  friction   clutch  in  to 
transmit    30  horse-power  at  200  revolutions  per  minute,  assuming 
working  radius  of  clutch  to  be  12  inches;  coefficient  of  friction  15 
per  cent;  angle  a  =10°  ? 

2.  How  much  horse-power  could  be  transmitted,  other  con- 
ditions remaining  the  same,  if  the  working  radius  were  increased 
to  18  inches  ? 

3.  What  force  would  be  necessary  in  problem  1,  if  the  angle 
a  were  15°,  other  conditions  remaining  the  same  ? 

COUPLINGS. 

DOTATION.— The  following  notation  is  used  throughout  the  chapter  on  Couplings: 

D  =  Diameter  of  shaft  (inches).  Sc  =Safe  crushing  fiber  stress  (Ibs.  per 
d    =Diameter  of  bolt  body  (inches).  sq.  in.). 

n    =  Number  of  bolts.  T  =Twisting  moment  (inch-lbs.). 
R  =  Radius  of  bolt  circle  (inches).  <=Thickness  of  flange  (inches). 

S  =Safe  shearing  fiber  stress  (Ibs.  per  W  =Load  on  bolts  (Ibs.). 
sq.  in.). 

ANALYSIS.  Kigid  couplings,  are  intended  to  make  the 
shafts  which  they  connect  act  as  a  solid,  continuous  shaft.  In 
order  that  the  shaft  may  be  worked  up  to  its  full  strength  capac- 
ity, the  coupling  must  be  as  strong  in  all  respects  as  the  shaft, 
or,  in  other  words,  it  must  transmit  the  same  torsional  moment. 
In  the  analysis  of  the  forces  which  come  upon  these  couplings,  it 
is  not  considered  that  they  are  to  take  any  side  load,  but  thr.t  they 
are  to  act  purely  as  torsional  elements.  It  is  doubtless  true  that  in 
many  cases  they  do  have  to  provide  some  side  strength  and  stiff- 
ness, but  this  is  not  their  natural  function,  nor  the  one  upon  which 
their  design  is  based. 


159 


146  MACHINE   DESIGN 


Referring  to  Fig.  51,  which  is  the  type  most  convenient  for 
analysis,  we  have  an  example  of  the  simplest  form  of  flange  coup- 
ling. It  consists  merely  of  hubs  keyed  to  the  two  portions,  with 
flanges  driving  through  shear  on  a  series  of  bolts  arranged  con- 
centrically about  the  shaft.  The  hubs,  keys,  and  tlanges  are  sub- 
]ect-  to  the  same  conditions  of  design  as  the  hubs,  keys,  and  web  of 
a  gear  or  pulley,  the  key  tending  to  shear  and  be  crushed  in  the 
hub  and  shaft,  and  the  hub  tending  to  be  torn  or  sheared  from  the 
flange.  The  driving  bolts,  which  must  be  carefully  fitted  in 
reamed  holes,  are  subject  to  a  purely  shearing  stress  over  their  full 
area  at  the  joint,  and  at  the  same  time  tend  to  crush  the  metal  in 
the  flange,  against  which  they  bear,  over  their  projected  area. 
This  latter  stress  is  seldom  of  importance,  the  thickness  of  the 
flange,  for  practical  reasons,  being  sufficient  to  make  the  crushing 
stress  very  low. 

THEORY.  The  theory  of  hubs,  keys,  and  flanges,  being  like 
that  already  given  for  pulleys  and  gears,  need  not  be  repeated  for 
couplings.  The  shearing  stress  on  the  bolts  is  the  only  new  point 
to  be  studied. 

In  Fig.  51,  for  a  twisting  moment  on  the  shaft  of  T,  the  load 

T 

at    the  bolt    circle  is   ~\Y  =  -r.       If   the   number   of  bolts  be;/. 
it 

equating  the  external  force  to  the  internal  strength,  we  have: 

T  S77Y/2 


Although  the  crushing  will  seldom  be  of  importance,  yet  for 
the  sake  of  completeness  its  equation  is  given,  thus: 

W=  ^-  =Sc(?tn.  (96) 

The   internal    moment    of    resistance    of    the    shaft    is  —  ^-  ; 

0.1 

hence  the  equation  representing  full  equality  of  strength  between 
the  shaft  and  the  coupling,  depending  upon  the  shearing  strength 
cf  the  bolts,  is: 

SD3         fern/2 


160 


MACHINE  DESIGN 


147 


The  theory  of  the  other  types  of  couplings  is  obscure,  except 
as  regards  the  proportions  of  the  key,  which  are  the  same  in  all 
cases.  The  shell  of  the  clamp  coupling,  Fig.  52,  should  be  thick 
enough  to  give  equal  torsional  strength  with  the  shaft;  but  the 
exact  function  which  the  bolts  perform  is  difficult  to  determine. 
In  general  the  bolts  clamp  the  coupling  tightly  on  the  shaft  and 
provide  rigidity,  but  the  key  does  the  principal  amount  of  the 
driving.  The  bolt  sizes,  in  these  couplings,  are  based  on  judgment 
and  relation  to  surrounding  parts,  rather  than  on  theory. 

PRACTICAL  HODIFICATION.  All  couplings  must  be  made 
with  care  and  nicely  fitted,  for  their  tendency,  otherwise,  is  to 


Fig.  52. 

spring  the  shafts  out  of  line.  In  the  case  of  the  flange  coupling, 
the  two  halves  may  be  keyed  in  place  on  the  shafts,  the  latter  then 
swung  on  centers  in  the  lathe,  and  the  joint  faced  off.  Thus  the 
joint  will  be  true  to  the  axis  of  the  shaft;  and,  when  it  is  clamped 
in  position  by  the  bolts,  no  springing  out  of  line  can  take  place. 

A  flange  F  (see  Fig.  51)  is  sometimes  made  on  this  form  of 
coupling,  in  order  to  guard  the  bolts.  It  may  be  used,  also,  to  take 
a  light  belt  for  driving  machinery;  but  a  side  load  is  thereby  thrown 
on  the  shaft  at  the  joint,  which  is  at  the  very  point  where  it  is  desir- 
able to  avoid  it. 

The  simplest  form  of  rigid  coupling  consists  of  a  plain  sleeve 
slipped  over  from  one  shaft  to  the  other,  when  the  second  is  butted 
up  against  the  first.  This  is  known  as  a  muff  coupling.  When 
'once  in  place,  this  is  a  very  excellent  coupling,  as  it  is  perfectly 
smooth  on  the  outside,  and  consists  of  the  fewest  possible  parts, 
merely  a  sleeve  and  a  key.  It  is,  however,  expensive  to  fi£, 


161 


148 


MACHINE  DESIGN 


difficult  to  remove,  and  requires   an   extra  space  of  half  its  length 
on  the  shaft  over  which  to  be  slipped  back. 

The  clamp  coupling  is  a  good  coupling  for  moderate- sized 
shafts,  where  the  flange  type  of  Fig.  51  would  be  unnecessarily 
expensive.  The  clam  p  coupling,  Fig.  52,  is  simply  a  muff  coupling 
split  in  halves,  and  recessed  for  bolts.  It  is  cheap  and  is  easily 
applied  and  removed,  even  with  a  crowded  shaft.  If  bored  with  a 
piece  of  paper  in  the  joint,  when  it  is  clamped  in  position  it  will 

iiinch  the  shaft  ti«ditly  and  make  a  rkml  connection.      It  is  desir- 

i  o      J  f-> 

able  to  have  the  bolt-heads  protected  as  much  as  possible,  and  this 
mav  be  accomplished  by  making  the  outside  diameter  lame  enough 

I  J  O  7"^  O 

so  that   the  bolts   will   not   project.      Often   an   additional   shell   is 
provided  to  encase  the  coupling  completely  after  it  is  located. 


n 


Fig.  53. 

There  are  many  other  special  forms  of  couplings,  some  of 
them  adjustable.  Most  of  them  depend  upon  a  wedging  action 
-xerte^d  by  taper  cones,  screws,  or  keys.  Trade  catalogues  are  to 
be  sought  for  their  description. 

The  claw  coupling,  Fig.  53,  is  nothing  but  a  heavy  flange 
coupling  with  interlocking  claws  or  jaws  on  the  faces  of  the  flano-es, 
to  take  the  place  of  the  driving  bolts.  This  coupling  can  be  thrown 
in  or  out  as  desired,  although  it  usually  performs  the  service  of  a 
rigid  coupling,  as  it  is  not  suited  toclutching-in  during  rapid  mo- 
tion, like  a  friction  clutch. 

Flexible  couplings,  which  allow  slight  lack  of  alignment,  are 
made  by  introducing  between  the  flanges  of  a  coupling  a  flexible 
disc,  the  one  flange  being  fastened  to  the  inner  circle  of  the  disc, 
the  other  to  the  outer  circle.  This  is  also  accomplished  by  pro- 
viding the  faces  of  the  flange  coupling  with  pins  that  drive  by 


162 


MACHINE  DESIGN 


149 


pressure  together  or  through  leather  straps  wrapped  round  the 
pins.  These  devices  are  mostly  of  a  special  and  often  uncertain 
nature,  lacking  the  positiveness  which  is  one  essential  feature 
of  a  good  coupling. 

PROBLEMS  ON  COUPLINGS. 

1.  A  flange  coupling  of  the  type  of  Fig.  51  is  used  on  a  shaft 
2  inches  is  diameter.     The  hub  is   3  inches  long,  and  carries  a 
standard  key,  of  proportions  indicated  below  in  the  table  of  "Pro- 
portions for  Gib  Keys"  (page  106).     The  bolt  circle  is  7  inches 
in  diameter,   and  it  is  desired  to   use  |-inch  bolts.     How  many 
bolts  are  needed  to  transmit  60,000  inch-lbs.,  for  a  fiber  stress  in 
the  bolt  of  6,000  ? 

2.  Using  6  bolts,  what  diameter  of  bolt  would  be  required  ? 

3.  If  four  |-inch  bolts  were  used  on  a  circle  of  8  inches  di- 
ameter, what  diameter  of  shaft  would  be  used   in  the  coupling  to 
give  equal  strength  with  the  bolts  ? 

BOLTS,  STUDS,  NUTS,  AND  SCREWS. 

NOTATION— The  following  notation  is  used   throughout  the  chapter  on  Bolts,  Studs, 
Nuts,  and  Screws: 


d    =  Diameter  of  bolt  (inches). 

di  =  Diameter  at  root  of  thread  (in- 
ches). 

H  =  Height  of  nut  (inches). 

I    =  Initial  axial  tension  (Ibs.). 

k   =  Allowable  bearing  pressure  on  sur- 
face of  thread  (Ibs,  per  sq.  in.). 

L  =  Lead,  or  distance  nut  advances 
along  axis  in  one  revolution 
(inches). 


I      =  Length  of  wrench  handle  (inches) 

B 
n     =  Number  of  threads  in  nut=  -. 

P    =  Axial  load  (Ibs.). 

;;  =  Pitch  of  thread,  or  distance  be- 
tween similar  points  on  adjacent 
threads,  measured  parallel  to 
axis  (inches). 

S    =  Fiber  stress  (Ibs.  per  sq.  in.). 

W  =  Load  on  bolt  (Ibs.). 


Fig.  54. 

ANALYSIS.  A  bolt  is  simply  a  cylindrical  bar  of  metal 
upset  at  one  end  to  form  a  head,  and  having  a  thread  at  the  other 
end,  Fig.  54.  A  stud  is  a  bolt  in  which  the  head  is  replaced  by 
a  thread;  or  it  is  a  cylindrical  bar  threaded  at  both  ends,  usually 


163 


150 


MACHINE  DESIGN 


having  a  small  plain  portion  in  the  middle,  Fig.  55.  The  object 
of  bolts  and  studs  is  to  clamp  machine  parts  together,  and  yet 
permit  these  same  parts  to  be  readily  disconnected.  The  bolt 
passes  through  the  pieces  to  be  connected,  and,  when  tightened, 
causes  surface  compression  between  the  parts,  while  the  reactions 
on  the  head  and  nut  produce  tension  in  the  bolt.  Studs  and  tap 
bolts  pass  through  one  of  the  connected  parts  and  are  screwed 
into  the  other,  the  stud  remaining  in  position  when  the  parts  are 
disconnected. 

As  all  materials  are  elastic  within  certain  limits,  the  action  of 


Fie.  55. 


Fig.  55«. 


a  bolt  in  clamping  two  machine  parts  together,  more  especially  if 
there  is  an  elastic  packing  between  them,  may  be  represented 
diagrammatically  by  Fig.  50,  in  which  a  spring  has  been  introduced 
to  take  the  compression  due  to  screwing  up  the  nut.  Evidently 
the  tension  in  the  bolt  is  equal  to  the  force  necessary  to  compress 
the  spring.  Now,  suppose  that  two  weights,  each  equal  to  i  W, 
are  placed  symmetrically  on  either  side  of  the  bolt,  then  the  tension 
in  the  bolt  will  be  increased  by  the  added  weights  if  the  bolt  is 
perfectly  rigid.  The  bolt,  however,  stretches;  hence  some  of  the 
compression  on  the  spring  is  relieved  and  the  total  tension  in  the 


164 


MACHINE  DESIGN 


151 


bolt  is  less  than  W  +  I,  by  an  amount  depending  on  the  relative 
elasticity  of  the  bolt  and  spring. 

Suppose  that  the  stud  in  Fig.  55  is  one  of  the  studs  connect- 
ing the  cover  to  the  cylinder  of  a  steam  engine,  and  that  the  studs 
have  a  small  initial  tension;  then  the  pressure  of  the  steam  loads 
each  stud,  and,  if  the  studs  stretch  enough  to  relieve  the  initial 
pressure  between  the  two  surfaces,  then  their  stress  is  due  to  the 
steam  pressure  only;  or,  from  Fig.  56,  when  I  =  W  ;  the  initial 
pressure  due  to  the  elasticity  of  the  joint  is  entirely  relieved  by  the 
assumed  stretch  of  the  studs.  Except  to  prevent  leakage,  it  is 
seldom  necessary  to  consider  the  initial  tension,  for  the  stretch 
of  the  bolt  may  be  counted  on  to  relieve 
this  force,  and  the  working  tension  on  the 
bolt  is  simply  the  load  applied. 

For  shocks  or  blows,  as  in  the  case 
of  the  bolts  found  on  the  marine  type  of 
connecting-rod  end,  the  stretch  of  the 
bolts  acts  like  a  spring  to  reduce  the  re- 
sulting tensions.  So  important  is  this 
feature  that  the  body  of  the  bolt  is  fre- 
quently turned  down  to  the  diameter  of 
the  bottom  of  the  thread,  thus  uniformly 
distributing  the  stretch  through  the  full 
length  of  the  bolt,  instead  of  localizing  it 
at  the  threaded  parts. 

In  tightening  up  a  bolt,  the  friction 
at  the  surface  of  the  thread  produces  a  twisting  moment,  which 
increases  the  stress  in  the  bolts,  just  as  in  the  case  of  shafting 
under  combined  tension  and  torsion;  but  the  increase  is  small  in 
amount,  and  may  readily  be  taken  care  of  by  permitting  low  values 
only  for  the  fiber  stress. 

In  a  flange  coupling,  bolts  are  acted  upon  by  forces  perpen- 
dicular to  the  axis,  and  hence  are  under  pure  shearing  stress.  If 
the  torque  on  the  shaft  becomes  too  great,  failure  will  occur  by 
the  bolts  shearing  off  at  the  joint  of  the  coupling. 

A  bolt  under  tension  communicates  its  load  to  the  nut  through 
the  locking  of  the  threads  together.  If  the  nut  is  thin,  and  the 
number  of  threads  to  take  the  load  few,  the  threads  may  break  or 


Fig.  56. 


165 


ID 2  MACHINE   DESIGN 


shear  off  at  the  root.  "With  a  V  thread  there  is  produced  a  com- 
ponent force,  perpendicular  to  the  axis  of  the  bolt,  which  tends  to 
split  the  nut. 

In  screws  for  continuous  transmission  of  motion  and  power. 
the  thread  may  be  compared  to  a  rough  inclined  plane,  on  which  a 
small  block,  the  nut,  is  being  pushed  upward  by  a  force  parallel  to 
the  base  of  the  plane.  The  angle  at  the  bottom  of  the  plane  is  the 
angle  of  the  helix,  or  an  angle  whose  tangent  is  the  lead  divided 
by  the  circumference  of  the  screw.  The  horizontal  force  corre- 
sponds to  the  tangential  force  on  the  screw.  The  friction  at  the 
surface  of  the  thread  produces  a  twisting  moment  about  the  axis  of 
the  screw,  which,  combined  with  the  axial  load,  subjects  the  screw 
to  combined  tension  and  torsion.  Screws  with  square  threads  are 
generally  used  for  this  service,  the  sides  of  the  thread  exerting  no 
bursting  pressure  on  the  nut.  The  proportions  of  screw  thread 
for  transmission  of  power  depend  more  on  the  bearing  pressure 
than  on  strength.  If  the  bearing  surface  be  too  small  and  lubrica- 
tion poor,  the  screw  will  cut  and  wear  rapidly. 

THEORY.  A  direct  tensile  stress  is  induced  in  a  bolt  when 
it  carries  a  load  exerted  along  its  axis.  This  load  must  be  taken 
by  the  section  of  the  bolt  at  the  bottom  of  the  thread.  If  the  area 

at  the  root  of  the  thread  is  -  —  ,  and  if  S  is  the  allowable   stress 

per    square    inch,    then    the    internal    resistance    of    the    bolt    is 

T'  '  .    Equating  the  external  load  to  the  internal  strength  we  have: 

.  (98) 


For  bolts  which  are  used  to  clamp  two  machine  parts  together 
so  that  they  will  not  separate  under  the  action  of  an  applied  load, 
the  initial  tension  of  the  bolt  must  be  at  least  equal  to  the  applied 
load.  If  the  applied  load  is  "W,  then  the  parts  are  just  about  to 
separate  when  I  =  "W.  Therefore  the  above  relation  for  strength 
is  applicable.  As  the  initial  tension  to  prevent  separation  should 
be  a  little  greater  than  "W,  a  value  of  S  should  be  chosen  so  that. 
there  will  be  a  margin  of  safety.  For  ordinary  wrought  iron  and 
steel,  S  may  be  taken  at  6,000  to  8,000. 


166 


MACHINE  DESIGN 


153 


If,  however,  the  joints  must  be  such  that  there  is  no  leakage 
between  the  surfaces,  as  in  the  case  of  a  steam  cylinder  head,  and 
supposing  that  elastic  packings  are  placed  in  the  joints,  then  a 
much  larger  margin  should  be  made,  for  the  maximum  load  which 
may  come  on  the  bolt  is  I  -f-  W,  where  "YV  is  the  proportional 
share  of  the  internal  pressure  carried  by  the  bolt.  In  such  cases 
S  =  3,000  to  5,000,  using  the  lower  value  for  bolts  of  less  than 
|-inch  diameter,.  - 

The  table  given  on  page  154  will  be  found  very  useful  in  pro- 
portioning bolts  with  U.  S.  standard  thread  for  any  desired  fiber 
stress. 

To  find  the  initial  tension  due  to  screwing  up  the  nut,  we 


Fig.  56a. 

may  assume  the  length  of  the  handle  of  an  ordinary  wrench,  meas- 
ured from  the  center  of  ths  bolt,  as  about  16  times  the  diameter 
of  the  bolt.  For  one  turn  of  the  wrench  a  force  F  at  the  handle 
would  pass  over  a  distance  2irl,  and  the  work  done  is  equal  to  the 
product  of  the  force  and  space,  or  F  X  %Trl.  At  the  same  time 
the  axial  load  P  would  be  moved  a  distance  p  along  the  axis. 
Assuming  that  there  is  no  friction,  the  equation  for  the  equality 
of  the  work  at  the  handle  and  at  the  screw  is: 


F27T/  = 


(99) 


Friction,  however,  is  always  present;  hence  the  ratio  of  the  useful 
work  (Pp)  to  the  work  applied  (F2irl)  is  not  unity  as  above  re- 


167 


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IV 


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•ut    'Tjs  .tod          x  —  i-Si^S 

H  S  ^ 

•s<i  i  ooo'i          --••-*  r  r:  r,  ?;  5  =£  ;;-:  t-2  g  s  --,  ^  --  i  r--  4!  x  -^  f,  s'  g  -.  |  g  =  g  |r 
IV 

Isl 

•tn  -bs  .tod         S  <"'  =  S  S  -2  3 

|l| 

•tit    -bs  .tad           «  VlS  So  2  3 

K 

•sai  ooo'S       ;    ~  -1  K  •  -  x  -  -  o  «  «  s  K  =  £  5  =  '-  .7!  x  ^  •_-  :-:  g  :-.  '£  -r  :t  p-  i:  -;  .--: 
IV                                                                                                                            '   ""- 

< 

•t,t-bsaod        SSrrSiiHs 

5V 

•P««IX 

.y 

jo   uionofl               _-"_-:  ri^i  re  ---'.-'^i-x^-'ri-^^rt 

< 

< 

•r-      ^-^-^^rKKSiiSSSSKSsHK 

•™«       *»/-*  VAV^VA'^M 

•qout  .tsd 


•  ^       CI        vsi       ~:        xct 


168 


MACHINE  DESIGN 


155 


lations  assume.  From  numerous  experiments  on  the  frict'on  of 
screws  and  nuts,  it  has  been  found  that  the  efficiency  may  be  as 
low  as  10  per  cent.  Introducing  the  efficiency  in  above  equation, 
it  may  be  written: 

?p          1 

TO     HF  (IOO) 

Assuming    that    50-  pounds   is    exerted    by   a    workman    in 


Fig.  58. 

tightening  up  the  nut  on  a  1-inch  bolt,  the  equation  above  shows 
that  P  =  4,021  pounds;  or  the  initial  tension  is  somewhat  less 
than  the  tabular  safe  load  shown  for  a  1-inch  bolt,  with  S  assumed 
at  10,000  pounds  per  sq.  inch. 

For  shearing  stresses  the  bolt  should  be  fitted  so  that  the  body 
of  the  bolt,  not  the  threads,  resists  the  force  tending  to  shear  off 
the  bolt  perpendicular  to  its  axis.  The  internal  strength  of  the 
bolt  to  resist  shear  is  the  allowable  stress  S  times  the  area  of  the 

bolt  in  shear,  or —  - —     If  W  represents  the  external  force  tending 

to  shear  the  bolt  the  equality  of  the  external  force  to  the  internal 
strength  is  : 

w=*5£.  (,oi) 


169 


150  MACHINE  DESIGN 

Reference  to  the  table  on  page  154  for  the  shearing  strength  of 
holts,  may  be  made  to  save  the  labor  of  calculations. 

Let  Fig.  58  represent  a  square  thread  screw  for  the  transmis- 
sion of  motion.  The  surface  on  which  the  axial  pressure  bears,  if 

//  is  the  number  of  threads  in  a  nut,  is (<72  —  <l\\    it.     Suppose 

that  a  pressure  of  /'  pounds  per  square  inch  is  allowed  on  the 
surface  of  the  thread.  Then  the  greatest  permissible  axial  load  1* 
must  not  exceed  the  allowable  pressure;  or,  equating, 

P  =  I-  _£  (<P  -  ^)  n  (102) 

The  value  of  1\'  varies  with  the  service  required.  If  the  motion  be 
slow  and  the  lubrication  very  good,  k  may  be  as  high  as  900.  For 
rapid  motion  and  doubtful  lubrication,  k  may  not  be  over  200. 
Between  these  extremes  the  designer  must  use  his  judgment, 
remembering  that  the  higher  the  speed  the  lower  is  the  allowable 
bearing  pressure. 

PRACTICAL  MODIFICATION.  It  will  be  noted  in  the 
formula'  for  holt  strengths  that  different  values  for  S  are  assumed. 
This  is  necessary  on  account  of  the  uncertain  initial  stresses  which 
are  produced  is  setting  up  the  nuts.  For  cases  of  mere  fastening, 
the  safe  tension  is  high,  as  just  before  the  joint  opens  the  tension 
is  about  equal  to  the  load  and  yet  the  fastening  is  secure.  On 
the  other- hand,  bolts  or  studs  fastening  joints  subjected  to  internal 
fluid  pressure  must  be  stressed  initially  to  a  greater  amount  than 
the  working  pressure  which  is  to  come  on  the  bolt.  As  this  initial 
stress  is  a  matter  of  judgment  on  the  part  of  the  workman,  the 
designer,  in  order  to  be  on  the  safe  side,  should  specify  not  less 
than  £-inch  or  :]-inch  bolts  for  ordinary  work,  so  that  the  bolts 
may  not  be  broken  off  by  a  careless  workman  accidentally  putting 
a  greater  force  than  necessary  on  the  wrench  handle.  In  making 
a  steam-tight  joint,  the  spacing  of  the  bolts  will  generally  deter- 
mine their  number;  hence  we  often  rind  an  excess  of  bolt  strength 
in  joints  of  this  character. 

Through  bolts  are  preferred  to  studs,  and  studs  to  tap.  bolts 
or  cap  screws.  I  f  possible,  the  design  should  be  such  that  through 
bolts  may  be  used.  They  are  cheapest,  are  always  in  standard 


170 


MACHINE  DESIGN  157 

stockj  and  well  resist  rough  usage  in  connecting  and  disconnecting. 
The  threads  in  cast  iron  are  weak  and  have  a  tendency  to  crumble; 
and  if  a  through  bolt  cannot  be  used  in  such  a  case,  a  stud,  which 
can  be  placed  in  position  once  for  all,  should  be  employed — not  a 
tap  bolt,  which  injures  the  thread  in  the  casting  every  time  it  is 
removed. 

The  plain  portion  of  a  stud  should  be  screwed  up  tight 
against  the  shoulder,  and  the  tapped  hole  should  be  deep  enough 
to  prevent  bottoming.  To  avoid  breaking  off  the  stud  at  the 
shoulder,  a  neck,  or  groove,  may  be  made  at  the  lower  end  of  the 
thread  entering  the  nut. 

To  withstand  shearing  forces  the  bolts  must  be  fitted  so  that 
no  lost  motion  may  occur,  otherwise  pure  shearing  will  not  be 
secured. 

Nuts  are  generally  made  hexagonal,  but  for  rough  work  are 
often  made  square.  The  hexagonal  nut  allows  the  wrench  to  turn 
through  a  smaller  angle  in  tightening  up,  and  is  preferred  to  the 
square  nut.  Experiments  and  calculations  show  that  the  height 
of  the  nut  with  standard  threads  may  be  about  |?  the  diameter  of 
the  bolt  and  still  have  the  shearing  strength  of  the  thread  equal  to 
the  tensile  strength  of  the  bolt  at  the  root  of  the  thread.  Practi- 

O 

cally,  however,  it  is  difficult  to  apply  such  a  thin  wrench  as  this 
proportion  would  call  for  on  ordinary  bolts.  More  commonly  the 
height  of  the  nut  is  made  equal  to  the  diameter  of  the  bolt  so  that 
the  length  of  thread  will  guide  the  nut  on  the  bolt,  give  a  low 
bearing  pressure  on  the  threads,  and  enable  a  suitable  wrench  to 
be  easily  applied.  The  standard  proportions  for  bolts  and  nuts 
may  be  found  in  any  handbook.  Not  all  manufacturers  conform 
to  the  United  States  standard;  nor  do  manufacturers  in  all  cases 
conform  to  one  another  in  practice. 

If  the  bolt  is  subject  to  vibration,  the  nuts  have  a  tendency  to 
loosen.  A  common  method  of  preventing  this  is  to  use  double 
nuts,  or  lock  nuts,  as  they  are  called  (see  Fig.  55  A).  The  under 
nut  is  screwed  tightly  against  the  surface,  and  held  by  a  wrench 
while  the  second  nut  is  screwed  down  tightly  against  the  first. 
The  effect  is  to  cause  the  threads  of  the  upper  nut  to  bear  against 
the  under  sides  of  the  threads  of  the  bolt.  The  load  on  the  bolt  is 
sustained  therefore  by  the  upper  nut,  which  should  be  the  thicker 


171 


158 


MACHINE  DESIGN 


of  the  two  ;  but  for  convenience  in  applying  wrenches  the  position 
of  the  nuts  is  often  reversed. 

The  form  of  thread  adapted  to  transmitting  power  is  the 
square  thread,  which,  although  giving  less  bursting  pressure 
on  the  nut,  is  not  as  strong  as  the  Y  thread  for  a  given  length, 
since  the  total  section  of  thread  at  the  bottom  is  only  ^  as  great. 
If  the  pressure  is  to  be  transmitted  in  but  one  direction,  the  two 


Fig.  59. 

types  may  be  combined  advantageously  to  form  tne  buttress  thread 
of  the  proportions  shown  in  Fig.  59.  Often,  as  in  the  carriage  of 
a  lathe,  to  allow  the  split  nut  to  be  opened  and  closed  over  the  lead 
screw,  the  sides  of  the  thread  are  placed  at  a  small  angle,  say  15", 
to  each  other,  as  illustrated  in  Fig.  60. 

The  practical  commercial  forms  in   which  wo    find   screwed 
fastenings  are  included  in  five  classes,  as  follows: 


|«      P'TCH 


1.  Through  bolts  (Fig.  61),  usually  rough  stock,  with  square 
upset  heads,  and  square  or  hexagonal  nuts. 

2.  Tap  bolts  (Fig.  62),  also  called  cap  screws.     These  usu- 
ally have  hexagonal  heads,  and  are  found  both  in  the  rough  form, 
and  finished  from  the  rolled  hexagonal  bar  in  the  screw  machine. 

3.  Studs  (Fig.  63),  rough  or  finished  stock,  threaded  in  the 
screw  machine. 

4.  Set  screws   (Fig.  64),  usually  with  square    heads,  and 
case-hardened  points.     Many  varieties  of  set  screws  are  made,  the 


172 


MACHINE  DESIGN 


159 


principal  distinguishing  feature  of  each  being  in  the  shape  of  the 
point.  Thus,  in  addition  to  the  plain  beveled  point,  we  find 
the  "  cupped,"  rounded,  conical,  and  "  teat "  points. 


Fig.  61.  Fig.  62.  Fig.  63. 

5.  Machine  screws  (Fig.  64«),  usually  round,  "  button," 
or  countersunk  head.  Common  proportions  are  indicated  relative 
to  diameter  of  body  of  screw. 


Fig.  64. 

PROBLEflS  ON  BOLTS,  STUDS,  NUTS,  AND  SCREWS. 

1.     Calculate    the   diameter  of   a  bolt   to  sustain  a  load  of 
5,000  Ibs. 


173 


1(50 


MACHINE  DESIGN 


2.  The  shearing  force  to  be  resisted  by  each  of  the  bolts  of  a 
flange  coupling  is  1,200  Ibs.     What  commercial   size  of  bolt  is 
required  ? 

3.  With  a  wrench  It)  times  the  diameter  of  the  bolt  and  an 
efficiency  of  10  per  cent,  what  axial  load  can  a  man  exert  on  a' 
standard  |-inch  bolt,  if  he  pulls  40  Ibs.  at  the  end  of  the  wrench 
handle? 

4.  A    single,  square- threaded   screw  of  diameter    2   inches, 
lead  j  inch,  depth  of  thread  £  inch,  length  of  nut   ;]  inches,  is  to 
be  allowed  a  bearing  pressure  of  HOO  Ibs.  per  square  inch.      What 
axial  load  can  be  carried  ( 

o.      Calculate  the  shearing  stress  at  the  root  of  the   thread  in 
problem  4. 


Fig.  64a. 

KEYS,  PINS,  AND  COTTERS. 

NOTATION  —The  following  notation  is  used  throughout  the  chapter  on  Keys,  Pins,  and 

Cotters: 


=  Average  diameter  of  rod  (inches). 
=  Outside   diameter   of     socket  (in- 
cies). 

of  shaft  (inches). 


r   =  Urivi 

PI  =  Axia 


Sc  =  Saf 


g  force  (Ibs.). 
oad  on  rod  (IDs.). 
s  at  which  I'  acts  (inches), 
rushing  fiber  stress  (Ibs. 


per  sq.  in.). 


SiT  =  Safe  shearing  liber  stress  (Ibs. 
per  sq.  in.). 

St  =Safe  tensile  fiber  stress  (Ibs.  per 
sq.  in.). 

T   =  Thickness  of  key  (inches). 

W  =  Width  of  key  (inches). 

w  =  Average  width  of  cotter  (inches). 

v"i  =  End  of  slot  to  end  of  rod  (inches). 

ir-2  =  End  of  slot  to  end  of  socket  (in- 
ches). 


KEYS  AND  PINS. 
ANALYSIS.      Keys    and    pins   are    used   to  prevent   relative 


174 


MACHINE  DESIGN  161 


rotary  motion  between  machine  parts  intended  to  act  together  as 
one  piece.  If  we  drill  completely  through  a  hub  and  across  the 
shaft,  and  insert  a  tightly  fitted  pin,  any  rotary  motion  of  the  one 
will  be  transmitted  to  the  other,  provided  the  pin  does  not  fail  by 
shearing  off  at  the  joint  between  the  shaft  and  the  hub.  The 
shearing  area  is  the  sum  of  the  cross -sections  of  the  pin  at  the 
joint. 

We  may  drill  a  hole  in  the  joint,  the  axis  of  the  hole  being 
parallel  to  the  axis  of  the  shaft,  and  drive  in  a  pin,  in  which  case 
we  introduce  a  shearing  area  as  before,  but  the  area  is  now  equal 
to  the  diameter  of  the  pin  multiplied  by  its  length,  and  the  pin  is 
stressed  sidewise,  instead  of  across.  It  is  evident  in  the  sidewise 
case  that  we  may  increase  the  shearing  area  to  anything  we  please, 
without  changing  the  diameter  of  the  pin,  merely  by  increasing 
the  length  of  the  pin. 

As  there  are  some  manufacturing  reasons  why  a  round  pin 
placed  lengthwise  in  the  joint  is  not  always  applicable,  we  may 
make  the  pin  a  rectangular  one,  in  which  case  it  is  called  a  key. 

When  pins  are  driven  across  the  shaft  as  in  the  first  instance, 
they  are  usually  made  taper.  This  is  because  it  is  easier  to  ream 
a  taper  hole  to  size  than  a  straight  hole,  and  a  taper  pin  will  drive 
more  easily  than  a  straight  pin,  it  not  being  necessary  to  match  the 
hole  in  hub  and  shaft  so  exactly  in  order  that  the  pin  may  enter. 
The  taper  pin  will  draw  the  holes  into  line  as  it  is  driven,  and  can 
be  backed  out  readily  in  removal. 

Keys  of  the  rectangular  form  are  either  straight  or  tapered, 
but  for  different  reasons  from  those  just  stated  for  pins.  Straight 
keys  have  working  bearing  only  at  the  sides,  driving  purely  by 
shear,  crushing  being  exerted  by  the  side  of  the  key  in  both  shaft 
and  hub,  over  the  area  against  the  key.  The  key  itself  does  not 
prevent  end  motion  along  the  shaft;  and  if  end  motion  is  not 
desired,  auxiliary  means  of  some  sort  must  be  resorted  to,  as,  for 
example,  set  screws  through  the  hub  jamming  hard  against  the  top 
of  the  key. 

If  end  motion  along  the  shaft  is  desired,  the  key  is  called  a 
spline,  and,  while  not  jammed  against  the  shaft,  is  yet  prevented 
from  changing  its  relation  to  the  hub  by  some  means  such  as 
illustrated  in  Fig.  65. 


175 


MACHINE  DESIGN 


Taper. keys  not  only  drive  through  sidewise  shearing  strength, 
but  prevent  endwise  motion  by  the  wedging  action  exerted  between 
the  shaft  and  hub.  These  keys  drive  more  like  a  strut  from  corner  to 
corner;  but  this  action  is  incidental  rather  than  intentional,  and  the 
proportions  of  a  taper  key  should  be  such  that  it  will  give  its  full 
resisting  area  in  shearing  and  crushing,  the  same  as  a  straight*  key. 


Fig.  65. 

THEORY.  Suppose  that  the  pin  illustrated  in  Fig.  66  passes 
through  hub  and  shaft,  and  the  driving  force  P  acts  at  the  radius 
R;  then  the  force  which  is  exerted  at  the  surface  of  the  shaft  to 

2  PR 

shear  off  the  pin  at  the  points  A  and  B  is ^ — .     If  D:  is  the 

average  diameter  of  the  pin,  its  shearing  strength  is    -     — - 1_. 

Equating  the  external  force  to  the  internal  strength,  we  have  : 
2PR        277-D,2  Ss 


4        ' 
|4PIT~ 

\    WST' 


(103) 


In  Fig.  67  a  rectangular   key  is  sunk  half  way  in  hub  and 
shaft  according  to  usual  practice.     Here  the  force  at  the  surface 


176 


MACHINE  DESIGN 


163 


of  the  shaft,  calculated  the  same  as  before,  not  only  tends  to  shear 
off  the  key  along  the  line  AB,  but  tends  to  crush  both  the  por- 
tion in  the  shaft  and  in  the  hub.  The  shearing  strength  along  the 


Fig.  66. 


Fig.  67. 


line  AB  is  LWSS.     Equating  external  force  to  internal  strength, 
we  have: 

2PR 

(.04) 


The  crushing  strength  is,  of  course,  that  due  to  the  weaker 
metal,  whether  in  shaft  or  hub.     Let  Sc  be  tnis  least  safe  crushing 

LT 

fiber  stress.     The  crushing  strength  then  is  —^-  Sc,  and,  equating 

external  force  to  internal  strength,  we  have: 
2PR      LT 


or, 


4PR 


(105) 


The  proportions  of  the  key  must  be  such  that  the  equations  as 
above,  both  for  shearing  and  for  crushing,  shall  be  satisfied. 

PRACTICAL  MODIFICATION.  Pins  across  the  shaft  can  be 
used  to  drive  light  work  only,  for  the  shearing  area  cannot  be  very 
large.  A  large  pin  cuts  away  too  much  area  of  the  shaft,  decreas- 
ing the  latter's  strength,  Pins  are  useful  in  preventing  end  motion, 
but  in  this  case  are  expected  to  take  no  shear,  and  may  be  of  small 


177 


104  MACHINE  DESIGN 

diameter.     The  common    split  pin   is  especially    adapted  to  this 
service,  and  is  a  standard  commercial  article. 

Taper  pins  are  usually  listed  according  to  the  Morse  standard 
taper,  proportions  of  which  may  be  found  in  any  handbook.  It 
is  desirable  to  use  standardise?  pins  in  machine  construction,  as 
the  reamers  are  a  commercial  article  of  accepted  value,  and  readily 
obtainable  in  the  machine-tool  market. 

AVith  properly  fitted  keys,  the  shearing  strength  is  usually 
the  controlling  element.  For  shafts  of  ordinary  size,  the  standard 
proportions  as  given  in  tables  like  that  below  are  safe  enough 
without  calculation,  up  to  the  limit  of  torsional  strength  of  the 
shaft.  For  special  cases  of  short  hubs  or  heavy  loads,  a  calcula- 
tion is  needed  to  check  the  size,  and  perhaps  modify  it. 

Splines,    also    known    as    '•  feather    k^ys."  require  thickness 
greater  than  regular  keys,  on  account  of  the 
slidincr  at  the  sides.     A  table  suggesting 
proportions  for  splines  is  given  on  page  lo'l>. 

Though  the  spline  may  be  either  in  th;- 
shaft  or  hub,  it  is  the  more  usual  thing  to 
lind  the  spline  dovetailed  (Fig.  G7'>), 
"gibbed."  or  otherwise  fastened  in  the 
hub;  and  a  long  spline  way  made  in  the 
shaft,  in  which  it  slides. 

The  straight  key,  accurately  fitted,  is  l^s-  ^~ul- 

the  most  desirable  fastening  device  for  ac- 
curate machines,  such  as  machine  tools,  on  account  of  the  fact  that 
there  is  absolutely  no  radial  force  exerted  to  throw  the  parts  out  of 
true.      It,  however,  requires  a  tight  lit  of  hub  to  shaft,  as  the  key 
cannot  be  relied  upon  to  take  up  any  looseness. 

The  taper  key  (Fig.  (">S),  by  its  wedging  action,  will  'take  up 
some  looseness,  but  in  so  doing  throws  the  parts  out  slightly. 
Or,  even  If  the  bored  fit  be  good,  if  the  taper  key  be  not  driven 
home  with  care,  it  will  spring  the  hub,  and  make  the  parts  run 
untrue.  The  great  advantage,  however,  that  the  taper  key  has  of 
holding  the  hub  from  endwise  motion,  renders  it  a  very  useful 
and  practical  article.  It  is  usually  provided  with  ahead,  or  "  gib." 
which  permits  a  draw  hook  to  be  used  to  wedge  between  the  face 
of  the  hub  and  the  key  to  facilitate  starting  the  key  from  its  seat. 


178 


MACHINE  DESIGN 


165 


Two  keys  at  90°  from  each  other  may  be  used  in  cases  where 
one  key  will  not  suffice.  The  fine  workmanship  involved  in 
spacing  these  keys  so  that  they  will  drive  equally  makes  this  plan 
inadvisable  except  in  case  of  positive  and  unavoidable  necessity. 

The  "  Woodruff "  key  (Fig.  69)  is  a  useful  patented  article 
for  certain  locations.  This  key  is  a  half-disc,  sunk  in  the  shaft 


_L 

H«       ,  TAPER 


PER  FT. 


1 


Fig.  68. 

and  the  hub  is  slipped  over  it.  A  simple  rotary  cutter  is  dropped 
into  the  shaft  to  produce  the  key  seat;  and  on  account  of  the 
depth  in  the  shaft,  the  tendency  to  rock  sidewise  is  eliminated, 
and  the  drive  is  purely  by  shear. 

Keys  may  be  milled  out  of  solid  stock,  or  drop-forged  to 
within  a  small  fraction  of  finished  size.  The  drop-forged  key  is 
an  excellent  modern  production  and  requires  but  a  minimum 


Fig.  69. 

amount  of  fitting.  Any  key,  no  matter  how  produced,  requires 
some  hand  fitting  and  draw  filing  to  bring  it  properly  to  its  seat 
and  give  it  full  bearing. 

It  is  good  mechanical  policy  to  avoid  keyed  fastenings 
whenever  possible.  This  does  not  mean  that  keys  may  never  be 
used,  but  that  a  key  is  not  an  ideal  way  to  produce  an  absolutely 
positive  drive,  partly  because  it  is  an  expensive  device,  and  partly 
because  the  tendency  of  any  key  is  to  work  itself  loose,  even  if 
carefully  fitted. 

The  following  tables  are  suggested  as  a  guide  to  proportions 


179 


100 


MACHINE  DESIGN 


of   <nb  keys  and  feather  key?,  and    will  be  found    useful    in   the 
absence  of  any  manufacturer's  standard  list: 

Fit-.  70.   PROPORTIONS  FOR  GIB  KEYS. 


Diameter  of  shaft  (rf),  inches. 

t!1!1* 

If 

2    2J;3i 

4 

5 

6J 

Width                     (W),  inches. 

T5Jf     T\ 

1 

T9ff 

«     I 

1TV 

!T5o 

If 

Thickness                (T).  inches. 

1     1     9    '     r>        13        7        1721 
4    '3  f\  T6    '$2    T"B  j  "ST1  32" 

If 

1 

^ 

Via.  11.   PROPORTIONS  FOR  FEATHER  KEYS. 


I 

Diameter  of  Shaft    (d),  inches,    I  !| 

1 

r, 

H 

2 

2i 

2}   3 

81 

4    4* 

Width                     CWi.  inches.    T\ 

A 

i 

i 

A  1 

i 

T9« 

A  i 

Thickness                (T),  inches.    1  J 

5 

T'i 

3 

8 

3 
8 

7 
T6 

i 

i 

1 

*       t_|l 

COTTERS. 

ANALYSIS.  (Jotters  are  used  to  fasten  hubs  to  rods  rather 
than  shafts,  the  distinction  between  a  rod  and  a  shaft  being  that 
a  rod  takes  its  load  in  the  direction  of  its  length,  and  does  not 
drive  by  rotation.  A  cotter,  therefore,  is  nothing  but  a  cross-pin 
of  modified  form,  to  take  shearing  and  crushing  stress  in  the 
direction  of  the  axis  of  the  rod.  instead  of  perpendicular  to  it. 

Referring  to  Fig.  72,  one  will  see  that  the  cotter  is  made 
long  and  thin — long,  in  order  to  get  sufficient  shearing  area  to  resist 
shearing  along  lines  A  and  B;  thin,  in  order  to  cut  as  little  cross- 
sectional  area  out  of  the  body  of  the  shaft  as  possible.  The  cotter 
itself  tends  to  shear  along  the  lines  A  and  B,  and  crush  along  the 
surfaces  K.  G,  and  .1.  The  socket  tends  to  crush  alono-  the  surfaces 

O 

K  and  G.  The  rod  end  D  tends  to  be  sheared  out  along  the  lines 
0  II  and  Q  E.  and  also  to  be  crushed  along  the  surface  J.  The 
socket  tends  to  be  sheared  aloncr  the  lines  V  U  and  X.  Y. 

o 

The  cotter  is  made  taper  on  one  side,  thus  enabling  it  to  draw 
up  the  flange  of  the  rod  tiVhtly  against  the  head  of  the  socket. 

O  J  O 

This  taper  must  not  be  great  enough  to  permit  easy  "backing  out" 
;md  loosening  of  the  cotter  under  load  or  vibration  in  the  rod.  In 
responsible  situations  this  cannot  be  safely  guarded  against  except 
through  some  auxiliary  locking  device,  such  as  lock  nuts  on  the 
end  of  the  cotter  (Fig.  73). 

THEORY.  Referring  to  Fig.  72,  assume  an  axial  load  of  Pt, 
as  shown.  The  successive  equations  of  external  force  to  internal 


180 


MACHINE  DESIGN 


167 


strength  are  enumerated  below,  for  the  different  actions  that  take 
place : 

For  shearing    along   lines  A  and  B,  w   being    the    average 
width  of  cotter,  and  Ss  safe  shearing  stress  of  cotter, 


j  =  2TwSs. 


(106) 


Fig.  72. 
For  crushing  along  surfaces  K  and  G,  S    being  least   safe 

O  O  <H 

crushing  stress,  whether  of  cotter  or  socket, 

(I07) 
fe  erne. 

\=.iyrs0.  (108) 


For  crushing  along  surface  J,  Sc  being  least  safe  crushing 
stress,  whether  of  cotter  or  socket, 


181 


MACHINE  DESIGN 


For  shearing  along  surfaces  CII  and  QE,  Ss  being  safe  shear 
in"1  stress  of  rod  end,  and  v,  end  of  slot  to  end  of  rod, 

l'i  =  ^DS,  (I09) 

For  tension  in  rod  end   at  section    across    slot,   St   being   safe 
tensile  stress  in  rod  end, 


(no) 


For  tension  in  socket  at  section  across  slot,  JSt  being  safe  ten- 
sile  stress  in  socket, 


(Hi) 


For  shearing  in  socket  along  the  lines  YU  and  XY,  S6  being 
safe1  shearing  stress  in  the  socket,  and  u\2  end  of  slot  to  end  of 
socket, 

P1  =  2w,(V1-T>)$s.  (112) 

The  ])roportions  of  cotter  and   socket   may    be    fixed    to   some 

extent  by  practical  or  as 
suraed  conditions.  The  di- 
mensions may  then  be  tested 
by  the  above  equations,  that 
the  safe  working  stresses  may 
not  be  exceeded,  the  dimen- 
sions being  then  modified  ac- 
cordingly. 

The  steel  of  which  both 
cotter  and  rod  would  ordina- 
rily be  made1  has  range  of 
working  iiber  stress  as 
follows  : 
Tension,  8,(XX)  to  1*2,(XX)  (Ibs.  pel 

sq.  in.) 
Compression,  10,000  to  10,000  (Ibs 

per  sq.  in.) 
Shear,   6,000  to   10,000   (Ibs.    per 

sq.  in.) 

The  socket,    if  made    of 
iron,  will  be  weak  as  regards  tension,  tendency  to  shear  out  at 


cast 


182 


MACHINE  DESIGN 


169 


the  end.  and  tendency  to  split.  The  uncertainty  of  cast  iron  to 
resist  these  is  so  great  that  the  hub  or  socket  must  be  very  clumsy 
in  order  to  have  enough  surplus  strength.  This  is  always  a  notice- 
able feature  of  the  cotter  type  of  fastening,  and  cannot  well  be 
avoided. 

PRACTICAL  MODIFICATION.  The  driving  faces  of  the  cot- 
ter are  often  made  semicircular.  This  not  only  gives  more  shear- 
ing area  at  the  sides  of  the  slots,  but  makes  the  production  of  the 
slots  easier  in  the  shop.  It  also  avoids  the  general  objection  to 
sharp  corners — namely,  a  tendency  to  start  cracks. 

A  practicable  taper  for 
cotters  is  ^  inch  per  foot. 
This  will  under  ordinary 
circumstances  prevent  the 
cotter  from  backing  out 
under  the  action  of  the  load. 
When  set  screws  against 
the  side  of  the  cotter,  or 


lock  nuts  are  used,  as  in 
Fig.  73,  the  taper  may  be 
greater  than  this,  perhaps 
as  much  as  li  inches  per 
foot. 

In  the  common  use  of 
the  cotter  for  holding  the  Fig.  74. 

strap  at  the  ends  of  con- 
necting rods,  the  strap  acts  like  a  modified  form  of  socket.  This  is 
shown  in  Figs.  73  and  74.  Here,  in  addition  to  holding  the  strap 
and  rod  together  lengthwise,  it  may  be  necessary  to  prevent  their 
spreading,  and  for  this  purpose  an  auxiliary  piece  G  with  gib  ends 
is  used.  The  tendency  without  this  extra  piece  is  shown  by  the 
dotted  lines  in  Fig.  74. 

The  general  mechanical  fault  with  cottered  joints  is  that  the 
action  of  the  load,  especially  \vhen  it  constantly  reverses,  as  in 
pump  piston  rods,  always  tends  to  work  the  cotter  loose.  Vibra- 
tion also  tends  to  produce  the  same  effect.  Once  this  looseness  is 
started  in  the  joint,  the  cotter  loses  its  pure  crushing  and  shearing 
action,  and  begins  to  partake  of  the  nature  of  a  hammer,  and 


183 


170  MACHINE  DESIGN 


pounds  itself  and  its  bearing  surfaces  out  of  their  true  shape. 
Instead  of  a  collar  on  the  rod,  we  often  find  a  taper  fit  of  the  rod 
in  the  socket;  and  any  looseness  in  this  case  is  still  worse,  for  the 
rod  then  has  end  play  in  the  socket,  and  by  its  "  shucking"  back 
and  forth  tends  to  split  open  the  socket. 

The  only  answer  to  these  objections  is  to  provide  a  positive 
locking  device,  and  take  up  any  looseness  the  instant  it  appears. 

PROBLEMS  ON  KEYS,  PINS,  AND  COTTERS. 

1.  Calculate  the  safe  load  in  shear  which  can  be  carried  on  a  key 
-A  inch  wide,  ^  inch  thick,  and  5  inches  long.      Assume  Ss  =  6,000. 

2.  Assuming  the  above  key  to  be  -j3fl  inch  in  hub  and-j3(]  inch 
in  shaft,  test  its  proportions  for  crushing,  at  Sc  =  16,000. 

3.  A  gear  60  inches  in   diameter  has  a  load  of  3,000  Ibs.  at 
the    pitch    line.     The    shaft  is    -i  inches  in  diameter,  in  a  hub, 
5    inches  long;  and  the  key  is  a  standard  gib  key  as  given  in  the 
table.     Test  its  proportions  for  shearing. 

4-.      A  piston  rod  2  inches  in  diameter  carries  a  cotter  §  inch 

J  O 

thick,  and  has  an  axial  load  of  20,000  Ibs.  Calculate  the  average 
width  of  the  cotter.  Ss  =  0,000. 

•3.      Calculate  fiber  stress    in    rod   in    preceding  problem    at 
section  through  slot. 

6.  How  far  from  the  end  of  rod  must  the  end  of  slot  be  ? 

7.  Calculate  the  crushing  fiber  stresses  on  cotter,  rod,  and 
socket. 

<S.     How  far  from  the  end  of  socket  must  the  end  of  slot  be, 
assuming  the  socket  to  be  of  steel  ? 

BEARINGS,  BRACKETS,  AND  STANDS. 

NOTATION— The  following  notation  is  used  throughout  the  chapters  on  Bearings 
Brackets,  and  Stands. 

A  =  Area  (square  inches).  Iv  = Number  of  revolutions  per  minute. 

n  =  Distance  between  bolt  centers  n  =  Number  of  bolts  in  cap. 

(inches).  >n—  Number  of  bolts  in  bracket  base. 

=  Width  of  bracket  base  (inches).  P  =  Total  pressure  on  bearing  (Ibs.). 

—  Distance  of  neutral  axis  from  outer  p  =  Pressure  per  square   inch  of  pro- 

liber  (inches).  jected  area  (Ibs). 

n  =  Diameter  of  shaft  (inches).  S  =  Safe  tensile  fiber  stress  (Ibs.). 

'/=  Diameter  of  bolt  body  (inches).  Ss  =    "     shearing      "  (Ibs.). 

<l\=  Diameter  at  root  of  thread  (inches).  T  = 'Total  load  on  bolts  at  top  of 
II  =  Horse-power.  bracket  (Ibs.), 

=  Thickness  of  cap  at  center  (inches).  t    =  Thickness  of  bracket  base  (inches). 

I  =   Moment  of  inertia.  x  =  Distance  from  line  of  action  of  load 
I,  =  Length  of  bearing  (inches).  to  any  section  of  bracket(inches). 

£A=  Coefficient  of  friction  (per  cent). 


184 


MACHINE  DESIGN  171 

ANALYSIS.  Machine  surfaces  taking  weight  and  pressure 
of  other  parts  in  motion  upon  them  are,  in  general,  known  as 
bearings.  If  the  motion  is  rectilinear,  the  bearing  is  termed  a 
slide,  guide,  or  way,  such  as  the  cross  slide  of  a  lathe,  the  cross- 
head  guide  of  a  steam  engine,  or  the  ways  of  a  lathe  bed. 

If  the  motion  is  a  rotary  one,  like  that  of  the  spindle  of  a  lathe, 
the  simple  word  "  bearing  "  is  generally  used. 

In  any  bearing,  sliding  or  rotary,  there  must  be  strength  to 
carry  the  load,  stiffness  to  distribute  the  pressure  evenly  over  the 
full  bearing  surface,  low  intensity  of  such  pressure  to  prevent  the 
lubricant  from  being  squeezed  out  and  to  minimize  the  wear,  and 
sufficient  radiating  surface  to  carry  away  the  heat  generated  by 
friction  of  the  surfaces  as  fast  as  it  is  generated.  Sliding  bearings 
are  of  such  varied  nature,  and  exist  under  conditions  so  peculiar 
to  each  case,  that  a  general  analysis  is  practically  impossible 
beyond  that  given  in  the  sentence  above. 

Rotary  bearings  can  be  more  definitely  studied,  as 'there  are 
but  two  variable  dimensions,  diameter  and  length,  and  it  is  the 
proper  relation  between  these  two  that  determines  a  good  bearing. 
The  size  of  the  shaft,  ^as  noted  under  "Shafts,"  is  calculated  by 
taking  the  bending  moment  at  the  center  of  the  bearing,  combin- 
ing it  with  the  twisting  moment,  and  solving  for  the  diameter 
consistent  with  the  assumed  fiber  stress.  But  this  size  must  then 
be  tried  for  deflection  due  to  the  bending  load,  in  order  that  the 
requirement  for  stiffness  may  be  fulfilled.  When  this  is  accom- 
plished, the  friction  at  the  bearing  surface  may  still  generate  so 
much  heat  that  the  exposed  surface  of  the  bearing  win  not  radiate 
it  as  fast  as  generated,  in  which  case  the  bearing  gets  hotter  and 
hotter,  until  it  finally  burns  out  the  lubricant  and  melts  the  lining 
of  the  bearing,  and  ruin  results. 

The  heat  condition  is  usually  the  critical  one,  as  it  is  very 
easy  to  make  a  short  bearing  which  is  strong  enough  and  amply 
stiff  for  the  load  it  carries,  but  which  nevertheless  is  a  failure  as 
a  bearing,  because  it  has  so  small  a  radiating  surface  that  it  can- 
not run  cool. 

The  side  load  which  causes  the  friction  and  the  consequent 
development  of  heat,  is  due  to  the  pull  of  the  belt  in  the  case  of 
pulleys,  the  load  on  the  teeth  or  gears,  the  puil  on  cranks  and 


185 


172  MACHINE  DESIGN 


levers,  the  weight  of  parts,  etc.  If  we  could  exert  pure  torsion  on 
shafts  without  any  side  pressure,  and  counteract  all  the  weight 
that  comes  on  the  shaft,  we  should  not  have  any  trouble  with  the 
development  of  heat  in  bearings;  in  fact,  there  would  theoretically 
be  no  need  of  bearings,  as  the  shafts  would  naturally  spin  about 
their  axes,  and  would  not  need  support. 

It  can  be  shown.,  theoretically,  that  the  radiating  surface  of  a 
bearing  increases  relatively  to  the  heat  generated  by  a  given  side 
load,  milij  'ii'Jicii  tJie  length  of  tit  e  heaving  v'.v  'tm-rc<ixt'il.  In  other 
words,  increasing  the  diameter  and  not  the  length,  theoretically 
increases  the  heat  generated  per  unit  of  time  just  as  much  as  it 
increases  the  radiating  surface;  hence  nothing  is  gained,  and  heat 
accumulates  in  the  bearing  as  before.  This  important  fact  is  veri- 
fied by  the  design  of  high-speed  bearings,  which,  it  is  always 
noted,  are  very  long  in  proportion  to  their  diameter,  thus  giving 
relatively  high  radiating  power. 

Bearings  must  be  rigidly  fastened  to  the  body  of  the  machine 
in  some  way,  and  the  immediate  support  is  termed  a  bracket, 
frame,  or  housing.  "Bracket"  is  a  very  general  term,  and  ap- 
plfes  to  the  supports  of  other  machine  parts  besides  ''bearings/' 
It  is  especially  applicable  to  the  more  familiar  types  of  bearing 
supports,  and  is  here  introduced  to  make  the  analysis  complete. 

The  bracket  must  be  strong  enough  as  a  beam  to  take  the 
side  load,  the  bending  moment  being  figured  at  such  points  as  are 
necessary  to  determine  its  outline.  It  may  be  of  solid,  box,  or 
ribbed  form,  the  latter  beino1  the  most  economical  of  material,  and 

o 

usually  permitting  the  simplest  pattern.  The  fastening  of  the 
bracket  to  the  main  body  of  the  machine  must  be  broad  to  give 
stability;  the  bolts  act  partly  in  shear  to  keep  the  bracket  from 
sliding  along  its  base,  and  partly  in  tension  to  resist  its  tendency 
to  rotate  about  some  one  of  its  edges,  due  to  the  side  pull  of  the 
belt,  gear  tooth,  or  lever  load,  as  the  case  may  be.  The  weight  of 
the  bracket  itself  and  of  the  parts  it  sustains  through  the  bearing, 
has  likewise  to  be  considered;  and  this  acts,  in  conjunction  with 
the  working  load  on  the  bearing,  to  modify  the  direction  and 
magnitude  of  the  resultant  load  on  the  bracket  and  its  fastening. 
Stands  are  forms  of  brackets,  and  are  subject  to  the  same 
analysis.  The  distinction  is  by  no  means  well  defined,  although 


186 


MACHINE  DESIGN 


173 


we  usually  think  moie  readily  of  a  stand  as  having  an  upright  or 
inverted  position  with  reference  to  the  ground.  The  ordinary 
"  hanger  "  is  a  good  example  of  an  inverted  stand;  and  the  regular 
"  floor  stand,"  found  on  jack  shafts  in  some  power  houses,  is  an 
example  of  the  general  class. 

THEORY.  As  the  method  of  calculation  of  the  diameter  of 
the  shaft,  as  well  as  its  deflection,  has  been  considered  under 
"  Shafts,"  we  may  assume  that  the  theoretical  study  of  bearings 
starts  on  a  given  basis  of  shaft  diameter  D.  The  main  problem 
then  being  one  of  heat  control,  let  us  first  calculate  the  amount  of 
heat  developed  in  a  bearing  by  a  given  side  load.  The  force  of 
friction  acts  at  the  circumference  of  the  shaft,  and  is  equal  to  the 
coefficient  of  friction  times  the  normal  force;  or,  for  a  given  side  load 
P,  Fig.  75,  the  force  of  friction 
would  be  jjiP.  The  peripheral 
speed  of  the  shaft  for  rN  revolu- 

7TDN 

.tions  per  minute  is  —  ^-     feet 

per  minute.     As  work  is  "  force 
times  distance,"  the  work  wasted 


in  friction  is  then 


foot- 


pounds per  minute.  One  horse- 
power being  equal  to  33,000  foot- 
pounds per  minute,  we  have  the 
equation, 


Fig.  75. 


~  12  X  33,000 

The  value  of  jLt  for  ordinary,  well -lubricated  bearings,  may  run  as 
low  as  5  per  cent;  but  as  the  lubrication  is  often  impaired,  it 
quite  commonly  rises  to  10  or  12  per  cent.  A  value  of  8  per  cent 
is  a  fair  average.  This  amount  of  horse-power  is  dissipated 
through  the  bearing  in  the  form  of  heat.  If  we  could  exactly 
determine  the  ability  that  each  particle  of  the  metal  around  the 
shaft  had  to  transmit  the  heat,  or  to  pass  it  along  to  the  outside 
of  the  casting,  and  if  we  could  then  determine  the  ability  of  the 
particles  of  air  surrounding  the  casting  to  receive  and  carry  away 


187 


174  MACHINE  DESIGN 


this  heat,  we  could  calculate  just  such  proportions  of  the  bearing 
and  its  casing  as  would  never  choke  or  retard  this  free  transfer  of 
heat  away  from  the  running  surface. 

Such  refined  theory  is  not  practical,  owing  to  the  complicated 
shapes  and  conditions  surrounding  the  bearing.  The  best  that  we 
can  do  is  to  say  that  for  the  usual  proportions  of  bearings  the  side 
load  may  exist  up  to  a  certain  intensity  of  "  pressure  per  square 
inch  of  projected  area  "  of  bearing,  or,  in  form  of  an  equation, 

P=pLD.  (n4) 

The  constant  j9  is  of  a  variable  nature,  depending  on  lubrication, 
speed,  air  contact,  and  other  special  conditions.  For  ordinary 
bearings  having  continuous  pressure  in  one  direction,  and  only 
fair  lubrication,  400  to  500  is  an  average  value.  When  the  pres- 
sure changes  direction  at  every'half-revolution,  the  lubricant  has 
a  better  chance  to  work  fully  over  the  bearing  surface,  and  a 
higher  value  is  permissible,  say,  500  to  800.  In  locations  where 
mere  oscillation  takes  place,  not  continuous  rotation,  and  reversal- 
of  pressure  occurs,  as  on  the  cross-head  pin  of  a  steam  engine,  p 
may  run  as  high  as  900  to  1,200.  On  the  crank  pins  of  locomo- 
tives, which  have  the  reversal  of  pressure,  and  the  benefit  of  high 
velocity  through  the  air  to  facilitate  cooling,  the  pressures  may  run 
equally  high.  On  the  eccentric  crank  pins  of  punching  and  shear- 
ing machines,  where  the  pressure  acts  only  for  a  brief  instant  and 
at  intervals,  the  pressure  ranges  still  higher  without  any  dangerous 
heating  action. 

When  a  bearing,  for  practical  reasons,  is  provided  with  a  cap 
held  in  place  by  bolts  or  studs,  the  tlieory  of  the  cap  and  bolts  is 
of  little  importance,  unless  the  load  comes  directly  against  the  rap 
and  bolts.  Except  in  the  latter  case,  the  proportions  of  the  cap  and 
the  size  of  the  bolts  are  dependent  upon  general  appearance 
and  utility,  it  being  manifestly  desirable  to  provide  a  substantial 
design,  even  though  some  excess  of  strength  is  thereby  introduced. 

For  the  worst  case  of  loading,  however,  which  is  when  the 
cap  is  acted  upon  by  the  direct  load,  such  as  P  in  Fig.  71),  we  have 
the  condition  of  a  centrally  loaded  beam  supported  at  the  bolts. 
It  is  probable  that  the  beam  is  partially  fixed  at  the  ends  by  the 
clamping  of  the  nut;  also  that  the  load  P,  instead  of  being  con- 


188 


MACHINE  DESIGN 


175 


centrated  at  the  center,  is  to  some  extent  distributed.    It  is  hardly 

Pa          Pa    , 

fair  to  assume  the  external   moment  equal   to  -~-  or  — j— ,  the  one 

being  too  small,  perhaps,  and  the  other  too  large.     It  will  be   rea- 
sonable to  take  the  external  moment  at  — p— ,  in  which  case,  equat- 


X 


Fig.  76. 
ing  tie  external  moment  to  the  internal  moment  of  resistance, 


Pa 
T 


SI 

6' 


SLA2 


from  which,  the  length  of  bearing  being  known,  we  may  calculate 
the  thickness  h. 

One  bolt  on  each  side  is  sufficient  for  bearings  not  more 
than  0  inches  long,  but  for  longer  bearings  we  usually  find  two 
bolts  'on  a  side.  The  theoretical  location  for  two  bolts  on  a  side, 
in  order  that  the  bearing  may  be  equally  strong  at  the  bolts  and 
at  the  center  of  the  length,  may  be  shown  by  the  principles  of 

mechanics    to  be  -^r  L  from   each  end,  as  indicated  in  Fig.  76. 
The  bolts  are  evidently  in  direct  tension,  and  if  equally  loaded 


189 


17(5  MACHINE  DESIGN 


would  each  take  their  fractional  share  of  the  whole  load  P.     This 

2 

is  difficult  to  <marantee,  and  it  is  safer  to  consider  that  -;r~  P  may 

o 

he  taken  by  the  holts  on  one  side.  On  this  hasis,  for  total  number 
of  bolts  //,  equating  the  external  force  to  the  internal  resistance  of 
the  holts,  we  have  : 


from  which  the  proper  commercial  diameter  may  be  readily  found. 
The  bracket  may  have  the  shape  shown  in  Fig.  77.  The 
portion  at  B  is  under  direct  shearing  stress;  and  if  A  be  the  area 
at  this  point,  and  Ss  the  safe  shearing  stress,  then,  equating  the 
external  force  to  the  internal  shearing  resistance, 

P=ASS.  (117) 

The  same  shear  comes  on  all  parts  of  the  bracket  to  the  left  of  the 
load,  but  there  is  an  excess  of  shearing  strength  at  these  points. 

At  the  point  of  fastening,  the  bolts  are  in  shear,  due  to  the 
same  load,  for  which  the  equation  is 

P  =  -^x,S,  (118) 

For  the  upper  bolts,  the  case  is  that  of  direct  tension,  assum- 
ing that  the  whole  bracket  tends  to  rotate  about  the  lower  edge  E. 
To  iind  the  load  T  on  these  bolts,  we  should  take  moments  about 
the  point  E,  as  follows: 

PL1=T/;orT=  ^  (119) 

Then,  equating  the  external  force  to  the  internal  resistance, 
T  =  ^  =  ^Xfs.  (.30) 

The  upper  flange  is  loaded  with  the  bolt  load  T,  and  tends  to 
break  off  at  the  point  of  connection  to  the  main  body  of  the 
bracket,  the  external  moment,  therefore,  being  T/'.  The  section 
of  the  flange  is  rectangular;  hence  the  equation  of  external  and  in- 
ternal moments  is: 


190 


MACHINE  DESIGN 


177 


=  -B-  (I2I> 

It  may  De  noted  that  the  lower  bolts  act  on  such  a  small  leverage 
about  E,  that  they  would  stretch  and  thus  permit  all  the  load  to 
be  thrown  on  the  upper  bolts;  this  is  the  reason  why  they  are  not 
subject  to  calculation  for  tension. 


.  —  b  —  . 

£ 

$ 

j 

•$- 

Fig.  77. 

The  section  of  the  bracket  to  the  left  of  the  load  P  is  depend- 
ent upon  the  bending  moment,  for,  if  this  section  is  large  enough 
to  take  the  bending  moment  properly,  the  shear  may  be  disregard- 
ed. It  should  be  calculated  at  several  points,  to  make  sure  that 
the  fiber  stress  is  within  allowable  limits.  The  general  expression 
for  the  equation  of  moments  is,  for  any  section  at  leverage  x, 

p*=£  (IM) 

from  which,   by   the    proper  substitution  of  the  moment  of  in- 


191 


178 


MACHINE  DESIGN 


ertia  of  the  section,  the  fiber  stress  can  be  calculated.  The  mo- 
ment of  inertia  for  simple  ribbed  sections  can  be  found  in  most 
handbooks.  The  process  of  solution  of  the  above  equation,  though 

simple,  is  apt  to  be  tedious, 
and  is  not  considered  neces- 
sary to  illustrate  here. 

PRACTICAL  MODIFI  = 
CATION.  Adjustment  is  an 
important  practical  feature  of 
bearings.  Unless  the  propor- 
tions are  so  ample  that  wear 
is  inappreciable,  simple  and 
ready  adjustment  must  be 
provided.  The  taper  bush- 
ing. Fig.  79,  is  neat  and  sat- 
isfactory for  machinery  in 
which  expense  and  refinement 
are  permissible.  This  is  true 
of  some  machine  tools,  but  is 
not  true  of  the  general  '•  run  "  of  bearings.  The  most  common 
form  of  adjustment  is  secured  by  the  plain  cap  (which  mayor  may 


Fig.  79. 


not  be  tongued  into  the  bracket),  with  liners  placed  in  -the  joint 
when  new,  which  may  subsequently  be  removed  or  reduced  so  as 
to  allow  the  cap  to  close  down  upon  the  shaft.  Several  forms  of 
cap  bearings  are  illustrated  in  Figs.  80,  81,  and  82. 


192 


MACHINE  DESIGN 


179 


Large  engine  shaft  bearings  have  special  forms  of  adjustment 
by  means  of  wedges  and  screws,  which  take  up  the  wear  in  all 
directions,  at  the  same  time  accurately  preserving  the  alignment 
of  the  shafts;  but  this  refinement  is  seldom  required  for  shafts  of 
ordinary  machinery. 

In  cases  where  the  cap  bearing  is  not  applicable,  a  simple 
bushing  may  be  used.  This  may  be  removed  when  worn,  and  a 


Fig.  80.  Fig.  81. 

new  one  inserted,  the  exact  alignment  being  maintained,  as  the 
outside  will  be  concentric  with  the  original  axis  of  shaft,  regard- 
less of  the  wear  which  has  taken  place  in  the  bore. 

The  lubrication  of  bearings  is  a  part  of  the  design,  in  that 
the  lubricant  should  be  intro- 
duced at  the  proper  point,  and 
pains  taken  to  guarantee  its  dis- 
tribution to  all  points  of  the  run- 
ning surface.  The  method  of 
lubrication  should  be  so  certain 
that  no  excuse  for  its  failure 
would  be  possible.  Grease  is  a 
successful  lubricator  for  heavy 
loads  and  slow  speeds,  oil  for 
light  loads  and  high  speeds. 

In  order  to  insure  the  lubri-  Fig.  82. 

cant  reaching   the  sliding    sur- 
faces and  entering  between  them,  it  must  be  introduced  at  a  point 


193 


ISO  MACHINE  DESIGN 


where  the  pressure  is  moderate,  and  where  the  motion  of  the  j tarts 
will  naturally  lead  it  to  all  points  of  the  bearing.  Grooves  and 
channels  of  ample  size  assist  in  this  regard.  A  special  form  of 
bearing  uses  a  ring  riding  on  the  shaft  to  carry  the  oil  constantly 
from  a  small  reservoir  beneath  the  shaft  up  to  the  top,  when-  it  is 
distributed  along  the  bearing  and  finally  Hows  back  to  the  reser- 
voir and  is  used  again. 

Tlu>  materials  of  which  bearings  are  made  vary  with  the 
service  required  and  with  the  refinement  of  the  bearing.  ( 'ast  iron 
makes  an  excellent  bearing  for  light  loads  and  slow  speeds,  but 
it  is  very  apt  to  "seize*'  the  shaft  in  case  the  lubrication  is  in  the 
least  degree  impaired.  Bronze,  in  its  many  forms. of  density  and 
hardness,  is  extensively  used  for  high-grade  bearings,  but  it  also 
has  little  natural  lubricating  power,  and  requires  careful  attention 
to  keep  it  in  good  condition. 

Babbitt,  a  composition  metal,  of  varying  degrees  of  hardness, 
is  the  most  universal  and  satisfactory  material  for  ordinary  bear- 
ings. It  affords  a  cheap  method  of  production,  being  poured  in 
molten  form  around  a  mandrel,  and  firmly  retained  in  its  casing  or 
shell  through  dovetailed  pockets  into  which  the  metal  flows  and 
hardens.  It  requires  no  boring  or  extensive  fitting.  Some 
scraping  to  uniform  bearing  is  necessary  in  most  cases,  but  this  is 
easily  and  cheaply  done.  Babbitt  is  a  durable  material,  and  has 
some  natural  lubricating  power,  so  that  it  has  less  tendency  to 
heat  with  scanty  lubrication  than  any  of  the  materials  previously 
mentioned.  Almost  any  grade  of  bearing  may  be  produced  writh 
babbitt.  In  its  finest  form  the  babbitt  is  hammered,  or  pened, 
into  the  shell  of  the  bearing,  and  then  bored  out  nearly  to  size,  a 
slightly  tapered  mandrel  being  subsequently  drawn  through,  com- 
pressing the  babbitt  and  giving  a  polished  surface. 

A  combination  bearing  of  babbitt  and  bronze  is  sometimes 
used.  In  this  the  bronze  lies  in  strips  from  end  to  end  of  the 
bearing,  and  the  babbitt  fills  in  between  the  strips.  The  shell, 
Deing  of  bronze,  gives  the  required  stiffness,  and  the  babbitt  the 
favorable  running  quality. 

PROBLEMS  ON  BEARINGS,    BRACKETS,  AND  STANDS. 

1.     Tiie  allowable  pressure  on  a  bearing  is  300  pounds  per 


194 


MACHINE  DESIGN  181 


square  inch  of  projected  area.  What  is  the  required  length  of 
the  bearing  if  the  total  load  is  4,500  pounds  and  the  diameter  is 
3  inches  ? 

2.  The  cross-head  pin  of  a  steam  engine  must  be  2.5  inches 
in  diameter  to  withstand  the  shearing  strain.     If  the  maximum 
pressure  is  10,000  pounds,  what  length  should  be  given  to  the  pin  ? 

3.  The  journals  on  the  tender  of  a  locomotive  are  8^  X  7 
inches.     The  total  weight  of  the  tender  and  load  is  60,000  pounds. 
If  there  are  8  journals,  what  is  the  pressure  per  square  inch  of 
projected  area  ? 

4.  What  horse-power  is  lost  in  friction  at  the  circumference 
of  a  3-inch  bearing  carry  ing  a  load  of  6,000  pounds,  if  the  number 
of  revolutions  per  minute  is  150  and  the  coefficient  of  friction  is 
assumed  to  be  5  per  cent  ? 

5.  The  cast-iron  bracket  in  Fig.   77  has  a  load  P  of  1,000 
pounds.     Determine  the  fiber  stress  in  the  web  section  at  the  base 
of  the    bracket  if  the  thickness  is  taken  at  ^  inch,  and  Lx  =  12 
inches;  I  =  20  inches;  k  =  11  inches;  t  =  1  inch. 

6.  Calculate    the   diameter   of  the  bolts  at  the  top  of  the 
bracket. 

7.  Assuming  r  equal  to  6  inches,  what  is  the  fiber  stress  at 
the  root  of  flange  ? 


195 


HOT    WATER    HEATER    AND    CONNECTIONS. 


HEATING  AND  VENTILATION 

PART   I 


SYSTEMS  OF  WARMING 

Any  system  of  warming  must  include,  first,  the  combustion 
of  fuel,  which  may  take  place  in  a  fireplace,  stove,  or  furnace,  or  a 
steam,  or  hot-water  boiler;  second,  a  system  of  transmission,  by  means 
of  which  the  heat  may  be  carried,  with  as  little  loss  as  possible,  to  the 
place  where  it  is  to  be  used  for  warming;  and  third,  a  system  of  dif- 
fusion, which  will  convey  the  heat  to  the  air  in  a  room,  and  to  its 
walls,  floors,  etc.,  in  the  most  economical  way. 

Stoves.  The  simplest  and  cheapest  form  of  heating  is  the  stove. 
The  heat  is  diffused  by  radiation  and  convection  directly  to  the  objects 
and  air  in  the  room,  and  no  special  system  of  transmission  is'required. 
The  stove  is  used  largely  in  the  country,  and  is  especially  adapted 
to  the  warming  of  small  dwelling-houses  and  isolated  rooms. 

Furnaces.  Next  in  cost  of  installation  and  in  simplicity  of 
operation,  is  the  hot-air  furnace.  In  this  method,  the  air  is  drawn 
over  heated  surfaces  and  then  transmitted  through  pipes,  while  at 
a  high  temperature,  to  the  rooms  where  heat  is  required.  'Furnaces 
are  used  largely  for  warming  dwelling-houses,  also  churches,  halls, 
and  schoolhouses  of  small  size.  They  are  more  costly  than  stoves, 
but  have  certain  advantages  over  that  form  of  heating.  They  require 
less  care,  as  several  rooms  may  be  warmed  from  a  single  furnace; 
and,  being  placed  in  the  basement,  more  space  is  available  in  the 
rooms  above,  and  the  dirt  and  litter  connected  with  the  care  of  a  stove 
are  largely  done  away  with. .  They  require  less  care,  as  only  one  fire 
is  necessary  to  warm  all  the  rooms  in  a  house  of  ordinary  size.  One 
great  advantage  in  the  furnace  method  of  warming  comes  from  the 
constant  supply  of  fresh  air  which  is  required  to  bring  the  heat  into 
the  rooms.  While  this  is  greatly  to  be  desired  from  a  sanitary  stand- 
point, it  calls  for  the  consumption  of  a  larger  amount  of  fuel  than 
would  otherwise  be  necessary.  This  is  true  because  heat  is  required 
to  warm  the  fresh  air  from  out  of  doors  up  to  the  temperature  of  the 


197 


HEATING  AND  VENTILATION 


rooms,  in  addition  to  replacing  the  heat  lost  by  leakage  and  conduction 
through  walls  and  windows. 

A  more  even  temperature  may  be  maintained  with  a  furnace 
than  by  the  use  of  stoves,  owing  to  the  greater  depth  and  size  of  the 
fire,  which  allows  it  to  be  more  easily  controlled. 

^  hen  a  building  is  placed  in  an  exposed  location,  there  is  often 
difficulty  in  warming  rooms  on  the  north  and  west  sides,  or  on  that 
side  toward  the  prevailing  winds.  This  may  be  overcome  to  some  ex- 
tent by  a  proper  location  of  the  furnace  and  by  the  use  of  extra  large 
pipes  for  conveying  the  hot  air  to  those  rooms  requiring  special  at- 
tention. 

Direct  Steam.  Direct  steam,  so  called,  is  widely  used  in  all 
classes  of  buildings,  both  by  itself  and  in  combination  with  other 
systems.  The  first  cost  of  installation  is  greater  than  for  a  furnace; 
but  the  amount  of  fuel  required  is  less,  as  no  outside  air  supply  is 
necessary.  If  used  for  warming  hospitals,  schoolhouses,  or  other 
buildings  where  a  generous  supply  of  fresh  air  is  desired,  this  method 
must  be  supplemented  by  some  form  of  ventilating  system. 

One  of  the  principal  advantages  of  direct  steam  is  the  ability 
to  heat  all  rooms  alike,  regardless  of  their  location  or  of  the  action 
of  winds. 

When  compared  with  hot-water  heating,  it  has  still  another 
desirable  feature — which  is  its  freedom  from  damage  by  the  freezing 
of  water  in  the  radiators  when  closed,  which  is  likely  to  happen  in 
unused  rooms  during  very  cold  weather  in  the  case  of  the  former 
system. 

On  the  other  hand,  the  sizes  of  the  radiators  must  be  proportioned 
for  warming  the  rooms  in  the  coldest  weather,  and  unfortunately 
there  is  no  satisfactory  method  of  regulating  the  amount  of  heat  in 
mild  weather,  except  by  shutting  off  or  turning  on  steam  in  the  radia- 
ators  at  more  or  less  frequent  intervals  as  may  be  required,  unless  one 
of  the  expensive  systems  of  automatic  control  is  employed.  In  large 
rooms,  a  certain  amount  of  regulation  can  be  secured  by  dividing 
the  radiation  into  two  or  more  parts,  so  that  different  combinations 
may  be  used  under  varying  conditions  of  outside  temperature.  If 
two  radiators  are  used,  their  surface  should  be  proportioned,  when 
convenient,  in  the  ratio  of  1  to  2,  in  which  case  one-third,  two-thirds, 
or  the  whole  power  of  the  radiation  can  be  used  as  desired. 


198 


HEATING  AND  VENTILATION 


Indirect  Steam.  This  system  of  heating  combines  some  of  the 
advantages  of  both  the  furnace  and  direct  steam,  but  is  more  costly 
to  install  than  either  of  these.  The  amount  of  fuel  required  is  about 
the  same  as  for  furnace  heating,  because  in  each  case  the  cool  fresh 
air  must  be  warmed  up  to  the  temperature  of  the  room,  before  it  can 
become  a  medium  for  conveying  heat  to  oifset  that  lost  by  leakage 
and  conduction  through  walls  and  windows. 

A  system  for  indirect  steam  may  be  so  designed  that  it  will  supply 
a  greater  quantity  of  fresh  air  than  the  ordinary  form  of  furnace,  in 
which  case  the  cost  of  fuel  will  of  course  be  increased  in  proportion  to 
the  volume  of  air  supplied.  Instead  of  placing  the  radiators  in  the 
rooms,  a  special  form  of  heater  is  supported  near  the  basement  ceiling 
and  encased  in  either  galvanized  iron  or  brick.  A  cold-air-  supply 
duct  is  connected  with  the  space  below  the  heater,  and  warm  air  pipes 
are  taken  from  the  top  and  connected  with  registers  in  the  rooms  to 
be  heated  the  same  as  in  the  case  of  furnace  heating. 

A  separate  stack  or  heater  may  be  provided  for  each  register  if 
the  rooms  are  large;  but,  if  small  and  so  located  that  they  may  be 
reached  by  short  runs  of  horizontal  pipe,  a  single  heater  may  serve 
for  two  or  more  rooms. 

The  advantage  of  indirect  steam  over  furnace  heating  comes  from 
the  fact  that  the  stacks  may  be  placed  at  or  near  the  bases  of  the  flues 
leading  to  the  different  rooms,  thus  doing  away  with  long,  horizontal 
runs  of  pipe,  and  counteracting  to  a  considerable  extent  the  effect  of 
wind  pressure  upon  exposed  rooms.  Indirect  and  direct  heating  are 
often  combined  to  advantage  by  using  the  former  for  the  more  import- 
ant rooms,  where  ventilation  is  desired,  and  the  latter  for  rooms  more 
remote  or  where  heat  only  is  required. 

Another  advantage  is  the  large  ratio  between  the  radiating  sur- 
face and  grate-area,  as  compared  with  a  furnace ;  this  results  in  a  large 
volume  of  air  being  warmed  to  a  moderate  temperature  instead  of  a 
smaller  quantity  being  heated  to  a  much  higher  temperature,  thus 
giving  a  more  agreeable  quality  to  the  air  and  rendering  it  less  dry. 

Indirect  steam  is  adapted  to  all  the  buildings  mentioned  in  con- 
nection with  furnace  heating,  and  may  be  used  to  much  better  advan- 
tage in  those  of  large  size.  This  applies  especially  to  cases  where 
more  than  one  furnace  is  necessary;  for,  with  steam  heat,  a  single 
boiler,  or  a  battery  of  boilers,  may  be  marie  to  supply  heat  for  a  build- 


199 


HEATING  AND  VENTILATION 


ing  of  any  she,  or  for  a  group  of  several  buildings,  if  desired,  and  is 
much  easier  to  care  for  than  several  furnaces  widely  scattered. 

Direct-Indirect  Radiators.  These  radiators  are  placed  in  the 
room  the  same  as  the  ordinary  direct  type.  The  construction  is  such 
that  when  the  sections  are  in  place,  small  flues  are  formed  between 
them;  and  air,  beirfg  admitted  through  an  opening  in  the  outside  wall, 
passes  upward  through  them  and  becomes  heated  before  entering  the 
room.  A  switch  damper  is  placed  in  the  casing  at  the  base  of  the 
radiator,  so  that  air  may  be  taken  from  the  room  itself  instead  of 
from  out  of  doors,  if  so  desired.  Radiators  of  this  kind  are  not  used 
to  any  great  extent,  as  there  is  likely  to  be  more  or  less  leakage  of  cold 
air  into  the  room  around  the  base.  If  ventilation  is  required,  it  is 
better  to  use  the  regular  form  of  indirect  heater  with  flue  and  register, 
if  possible.  It  is  sometimes  desirable  to  partially  ventilate  an  isolated 
room  where  it  would  be  impossible  to  run  a  flue,  and  in  cases  of  this 
kind  the  direct-indirect  form  is  often  useful. 

Direct  Hot  Water.  Hot  water  is  especially  adapted  to  the  warm- 
ing of  dwellings  and  greenhouses,  owing  to  the  ease  with  which  the 
temperature  can  be  regulated.  ^Yhen  steam  is  used,  the  radiators  are 
always  at  practically  the  same  temperature,  while  with  hot  water  the 
temperature  can  be  varied  at  will.  A  system  for  hot-water  heating 
costs  more  to  install  than  one  for  steam,  as  the  radiators  must  be  larger 
and  the  pipes  .more  carefully  run.  On  the  other  hand,  the  cost  of 
operating  is  somewhat  less,  because  the  water  need  be  carried  only  at 
a  temperature  suflicientlv  high  to  warm  the  rooms  properly  in  mild 
weather,  while  with  steam  the  building  is  likely  to  become  overheated, 
and  more  or  less  heat  wasted  through  open  doors  and  windows. 

A  comparison  of  the  relative  costs  of  installing  and  operating  hot- 
air,  steam,  and  hot-water  systems,  is  given  in  Table  I. 

TABLE  I 
Relative  Cost  of  Heating  Systems 


HOT  Am 

STEAM 

HOT  WATER 

Relative  cost  of  apparatus                                       9 

13 

15 

Relative  cost,  adding  repairs  and  fuel 

for  five  years                                                         29* 

29? 

27 

Relative  cost,  adding  repairs  and  fuel  for 

fifteen  years                                                          SI 

63 

52^ 

200 


HEATING  AND  VENTILATION 


One  disadvantage  in  the  use  of  hot  water  is  the  danger  from 
freezing  when  radiators  are  shut  off  in  unused  rooms.  This  makes 
it  necessary  in  very  cold  weather  to  have  all  parts  of  the  system  turned 
on  sufficiently  to  produce  a  circulation,  even  if  very  slow.  This  is 
sometimes  accomplished  by  drilling  a  very  small  hole  (about  |  inch) 
in  the  valve-seat,  to  that  when  closed  there  will  still  be  a  very  slow 
circulation  through  the  radiator,  thus  preventing  the  temperature  of 
the  water  from  reaching  the  freezing  point.  • 

Indirect  Hot  Water.  This  is  used  under  the  same  conditions  as 
indirect  steam,  but  more  especially  in  the  case  of  dwellings  and  hospi- 
tals. When  applied  to  other  and  larger  buildings,  it  is  customary  to 
force  the  water  through  the  mains  by  means  of  a  pump.  Larger 
heating  stacks  and  supply  pipes  are  required  than  for  steam;  but  the 
arrangement  and  size  of  air-flues  and  registers  are  practically  the 
same,  although  they  are  sometimes  made  slightly  larger  in  special  cases, 

Exhaust  Steam.  Exhaust  steam  is  used  for  heating  in  connection 
with  power  plants,  as  in  shops  and  factories,  or  in  office  buildings 
which  have  their  own  lighting  plants.  There  are  two  methods  of 
using  exhaust  steam  for  heating  purposes.  One  is  to  carry  a  back 
pressure  of  2  to  5  pounds  on  the  engines,  depending  upon  the  length 
and  size  of  the  pipe  mains ;  and  the  other  is  to  use  some  form  of  vacuum 
system  attached  to  the  returns  or  air-valves,  which  tends  to  reduce 
the  back  pressure  rather  than  to  increase  it. 

Where  the  first  method  is  used  and  a  back  pressure  carried,  either 
the  boiler  pressure  or  the  cut-off  of  the  engines  must  be  increased,  to 
keep  the  mean  effective  pressure  the  same  and  not  reduce  the  horse- 
power delivered.  In  general  it  is  more  economical  to  utilize  the  ex- 
haust steam  for  heating.  There  are  instances,  however,  where  the 
relation  between  the  quantities  of  steam  required  for  heating  and  for 
power  are  such — especially  if  the  engines  are  run  condensing — that 
it  is  better  to  throw  the  exhaust  away  and  heat  with  live  steam. 
Where  the  vacuum  method  is  used,  these  difficulties  are  avoided ;  and 
for  this  reason  that  method  is  coming  into  quite  common  use. 
If  the  condensation  from  the  exhaust  steam  is  returned  to  the 
boilers,  the  oil  must  first  be  removed ;  this  is  usually  accomplished  by 
passing  the  steam  through  some  form  of  grease  extractor  as  it  leaves 
the  engine.  The  water  of  condensation  is  often  passed  through  a 
separating  tank  in  addition  to  this,  before  it  is  delivered  to  the  return 


201 


fl  HEATING  AND  VENTILATION 

pumps.  It  is  bettor,  however,  to  remove  a  portion  of  the  oil  before 
the  steam  enters  the  heating  system ;  otherwise  a  coating  will  be  formed 
upon  the  inner  surfaces  of  the  radiators,  which  will  reduce  their 
efficiency  to  some  extent. 

Forced  Blast.  This  method  of  heating,  in  different  forms,  is 
used  for  the  warming  of  factories,  schools,  churches,  theaters,  halls — 
in  <fact,  any  large  building  where  good  ventilation  is  desired.  The 
air  for  warming  is  drawn  or  forced  through  a  heater  of  special  design, 
and  discharged  by  a  fan  or  blower  into  ducts  .which  lead  to  registers 
placed  in  the  rooms  to  be  warmed.  The  heater  is  usually  made  up  in 
sections,  so  that  steam  may  be  admitted  to  or  shut  off  from  any  section 
independently  of  the  others,  and  the  temperature  of  the  air  regulated 
in  this  manner.  Sometimes  a  by-pass  damper  is  attached,  so  that 
part  of  the  air  will  pass  through  the  heater  and  part  around  or  over  it; 
in  this  way  the  proportions  of  cold  and  heated  air  may  be  so  adjusted 
as  to  give  the  desired  temperature  to  the  air  entering  the  rooms.  These 
forms  of  regulation  are  common  where  a  blower  is  used  for  warming 
a  single  room,  as  in  the  case  of  a  church  or  hall;  but  where  several 
rooms  are  warmed,  as  in  a  schoolhouse.  it  is  customary  to  use  the 
main  or  primary  heater  at  the  blower  for  warming  the  air  to  a  given 
temperature  (somewhat  below  that  which  is  actually  required),  and 
to  supplement  this  by  placing  secondary  coils  or  heaters  at  the  bottoms 
of  the  flues  leading  to  the  different  rooms.  By  means  of  this  arrange- 
ment, the  temperature  of  each  room  can  be  regulated  independently 
of  the  others.  The  so-called  double-duct  system  is  sometimes  employed. 
In  this  case,  two  ducts  are  carried  to  each  register,  one  supplying  hot 
air  and  the  other  cold  or  tempered  air;  and  a  damper  for  mixing  these 
in  the  right  proportions  is  placed  in  the  flue,  below  the  register. 

Electric  Heating.  Unless  electricity  can  be  produced  at  a  very 
low  cost,  it  is  not  practicable  for  heating  residences  or  large  buildings. 
The  electric  heater,  however,  has  quite  a  wide  field  of  application  in- 
heating  small  offices,  bathrooms,  electric  cars,  etc.  It  is  a  convenient 
method  of  warming  isolated  rooms  on  cold  mornings,  in  late  spring  and 
earlv  fall,  when  the  regular  heating  apparatus  of  the  building  is  not  in 
operation.  It  has  the  advantage  of  being  instantly  available,  and  the 
amount  of  heat  can  be  regulated  at  will.  Electric  heaters  are  clean, 
do  not  vitiate  the  air,  and  are  easily  moved  from  place  to  place. 


202 


HEATING  AND  VENTILATION  f 

PRINCIPLES    OF    VENTILATION 

Closely  connected  with  the  subject  of  heating  is  the  problem  of 
maintaining  air  of  a  certain  standard  of  purity  in  the  various  buildings 
occupied. 

The  introduction  of  pure  air  can  be  done  properly  only  in  con- 
nection with  some  system  of  heating;  and  no  system  of  heating  is 
complete  without  a  supply  of  pure  air,  depending  in  amount  upon  the 
kind  of  building  and  the  purpose  for  which  it  is  used. 

Composition  of  the  Atmosphere.  Atmospheric  air  is  not  a  simple 
substance  but  a  mechanical  mixture.  Oxygen  and  nitrogen,  the 
principal  constituents,  are  present  in  very  nearly  the  proportion  of  one 
part  of  oxygen  to  four  parts  of  nitrogen  by  weight.  Carbonic  acid  gas, 
the  product  of  all  combustion,  exists  in  the  proportion  of  3  to  5  parts 
in  10,000  in  the  open  country.  Water  in  the  form  of  vapor,  varies 
greatly  with  the  temperature  and  with  the  exposure  of  the  air  to  open 
bodies  of  water.  In  addition  to  the  above,  there  are  generally  present, 
in  variable  but  exceedingly  small  quantities,  ammonia,  sulphuretted 
hydrogen,  sulphuric,  sulphurous,  nitric,  and  nitrous  acids,  floating 
organic  and  inorganic  matter,  and  local  impurities.  Air  also  contains 
ozone,  which  is  a  peculiarly  active  form  of  oxygen ;  and  lately  another 
constituent  called  argon  has  been  discovered. 

Oxygen  is  the  most  important  element  of  the  air,  so  far  as  both 
heating  and  ventilation  are  concerned.  It  is  the  active  element  in  the 
chemical  process  of  combustion  and  also  in  the  somewhat  similar 
process  which  takes  place  in  the  respiration  of  human  beings.  Taken 
into  the  lungs,  it  acts  upon  the  excess  of  carbon  in  the  blood,  and  pos- 
sibly upon  other  ingredients,  forming  chemical  compounds  which  are 
thrown  off  in  the  act  of  respiration  or  breathing. 

Nitrogen.  The  principal  bulk  of  the  atmosphere  is  nitrogen, 
which  exists  uniformly  diffused  with  oxygen  and  carbonic  acid  gas. 
This  element  is  practically  inert  in  all  processes  of  combustion  or 
respiration.  It  is  not  affected  in  composition,  either  bypassing  through 
a  furnace  during  combustion  or  through  the  lungs  in  the  process  of 
respiration.  Its  action  is  to  render  the  oxygen  less  active,  and  to 
absorb  some  part  of  the  heat  produced  by  the  process  of  oxidation. 

Carbonic  acid  gas  is  of  itself  only  a  neutral  constituent  of  the 
atmosphere,  like  nitrogen ;  and — contrary  to  the  general  impression — 
its  presence  in  moderately  large  quantities  (if  uncombined  with  other 


203 


HEATING  AND  VENTILATION 


substances)  is  neither  disagreeable  nor  especially  harmful.  Its 
presence,  however,  in  air  provided  for  respiration,  decreases  the  readi- 
ness with  which  the  carbon  of  the  blood  unites  with  the  oxygen  of  the 
air;  and  therefore,  when  present  in  sufficient  quantity,  it  may  cause 
indirectly,  not  only  serious,  but  fatal  results.  The  real  harm  of  a 
vitiated  atmosphere,  however,  is  caused  by  the  other  constituent 
gases  and  by  the  minute  organisms  which  are  produced  in  the  process 
of  respiration.  It  is  known  that  these  other  impurities  exist  in  fixed 
proportion  to  the  amount  of  carbonic  acid  present  in  an  atmosphere 
vitiated  by  respiration.  Therefore,  as  the  relative  proportion  of 
carbonic  acid  can  easily  be  determined  by  experiment,  the  fixing  of  a 
standard  limit  of  the  amount  in  which  it  may  be  allowed,  also  limits  the 
amounts  of  other  impurities  which  are  found  in  combination  with  it. 

When  carbonic  acid  is  present  in  excess  of  10  parts  in  10,000 
parts  of  air,  a  feeling  of  weariness  and  stuffiness,  generally  accompanied 
by  a  headache,  will  be  experienced;  \vhile  with  even  8  parts  in  10,000 
parts  a  room  would  be  considered  close.  For  general  considerations 
of  ventilation,  the  limit  should  be  placed  at  0  to  7  parts  in  10,000,  thus 
allowing  an  increase  of  2  to  3  parts  over  that  present  in, outdoor  air, 
which  may  be  considered  to  contain  four  parts  in  10,000  under  ordi- 
nary conditions. 

Analysis  of  Air.  An  accurate  qualitative  and  quantitative 
analysis  of  air  samples  can  be  made  only  by  an  experienced  chemist. 
There  are,  however,  several  approximate  methods  for  determining 
the  amount  of  carbonic  acid  present,  which  are  sufficiently  exact  for 
practical  purposes.  Among  these  the  following  is  one  of  the  simplest : 

The  necessary  apparatus  consists  of  six  clean,  dry,  and  tightly 
corked  bottles,  containing  respectively  100,  200,  250, 300,  350,  and  400 
cubic  centimeters,  a  glass  tube  containing  exactly  15  cubic  centimeters 
to  a  given  mark,  and  a  bottle  of  perfectly  clear,  fresh  limewater.  The 
bottles  should  be  filled  with  the  air  to  be  examined  by  means  of  a  hand- 
ball syringe.  Add  to  the  smallest  bottle  15  cubic  centimeters  of  the 
limewater,  put  in  the  cork,  and  shake  well.  If  the  limewater  has  a 
milky  appearance,  the  amount  of  carbonic  acid  will  be  at  least  16 
parts  in  10,000.  If  the  contents  of  the  bottle  remain  clear,  treat  the 
bottle  of  200  cubic  centimeters  in  the  same  manner;  a  milky  appear- 
ance or  turbidity  in  this  would  indicate  12  parts  in  10,000.  In  a 
similar  manner,  turbidity  in  the  250  cubic  centimeter  bottle  indicates 


204 


HEATING  AND  VENTILATION  9 

10  parts  in  10,000;  in  the  300,  8  parts;  in  the  350,  7  parts;  and  in  the 
400,  less  than  6  parts.  The  ability  to  conduct  more  accurate  analyses 
can  be  attained  only  by  special  study  and  a  knowledge  of  chemical 
properties  and  of  methods  of  investigation. 

Another  method  similar  to  the  above,  makes  use  of  a  glass 
cylinder  containing  a  given  quantity  of  limewater  and  provided  with  a 
piston.  A  sample  of  the  air  to  be  tested  is  drawn  into  the  cylinder  by 
an  upward  movement  of  the  piston.  The  cylinder  is  then  thoroughly 
•shaken,  and  if  the  limewater  shows  a  milky  appearance,  it  indicates 
a  certain  proportion  of  carbonic  acid  in  the  air.  If  the  limewater 
remains  clear,  the  air  is  forced  out,  and  another  cylinder  full  drawn  in, 
the  operation  being  repeated  until  the  limewater  becomes  milky. 
The  size  of  the  cylinder  and  the  quantity  of  limewater  are  so  propor- 
tioned that  a  change  in  color  at  the  first,  second,  third,  etc.,  cylinder 
full  of  air  indicates  different  proportions  of  carbonic  acid.  This  test 
is  really  the  same  in  principle  as  the  one  previously  described;  but  the 
apparatus  used  is  in  more  convenient  form. 

Air  Required  for  Ventilation.  The  amount  of  air  required  to 
maintain  any  given  standard  of  purity  can  very  easily  be  determined, 
provided  we  know  the  amount  of  carbonic  acid  given  off  in  the  process 
of  respiration.  It  has  been  found  by  experiment  that  the  average 
production  of  carbonic  acid  by  an  adult  at  rest  is  about  .6  cubic  foot 
per  hour.  If  we  assume  the  proportion  of  this  gas  as  4  parts  in  10,000 
in  the  external  air,  and  are  to  allow  6  parts  in  10,000  in  an  occupied 
room,  the  gain  will  be  2  parts  in  10,000;  or,  in  other  words,  there  will 

2 
be  =  .0002  cubic  foot  of  carbonic  acid  mixed  with  each  cubic 


foot  of  fresrf  air  entering  the  room.  Therefore,  if  one  person  gives 
off  .6  cubic  foot  of  carbonic  acid  per  hour,  it  will  require  .6  -r-  .0002 
=*  3,000  cubic  feet  of  air  per  hour  per  person  to  keep  the  air  in  the 
room  at  the  standard  of  purity  assumed  —  that  is,  6  parts  of  carbonic 
acid  in  10,000  of  air. 

Table  II  has  been  computed  in  this  manner,  and  shows  the 
amount  of  air  which  must  be  introduced  for  each  person  in  order  to 
maintain  various  standards  of  purity. 

While  this  table  gives  the  theoretical  quantities  of  air  required 
for  different  standards  of  purity,  and  may  be  used  as  a  guide,  it  will  be 
better  in  actual  practice  to  use  quantities  which  experience  has  shown 


205 


10 


HEATING  AND  VENTILATION 


to  give  good  results  in  different  types  of  buildings.  In  auditoriums 
where  the  cubic  space  per  individual  is  large,  and  in  which  the  atmos- 
phere is  thoroughly  fresh  before  the  rooms  are  occupied,  and  the 
occupancy  is  of  only  two  or  three  hours'  duration,  the  air-supply  may 
be  reduced  somewhat  from  the  figures  given  below. 

TABLE  II 
Quantity  of  Air  Required  per  Person 


STANDARD  PARTS  OF  CARBONIC 
ACID  IN  10,000  OF  AIR 


CUBIC  FEET  OF  AIR  REQUIRED  PER  PERSON 


INR°OM                                     Per  Minute 

Per  Hour 

5 

100 

6,000 

G 

50 

3,000 

7 

33 

2,000 

8 

25 

1,500 

9 

20 

1,200 

10 

•      16 

1,000 

Table  III  represents  good  modern  practice  and  may  be  used 
with  satisfactory  results : 

TABLE  III 
Air  Required  for  Ventilation  of  Various  Classes  of  Buildings 


CUBIC  FEET   PER 


AIR-SUPPLY  PER  OCCUPANT  FOR 

MlNUlE 

HOUR 

Hospitals 

80  to  100 

4,  800  to  6,  000 

High  Schools 

50 

3,  000 

Grammar  Schools 

40 

2,  400 

Theaters  and  Assembly  Halls 

25 

1  ,  500 

Churches 

20 

1,200 

CUBIC  FEET  PER 


When  possible,  the  air-supply  to  any  given  room  should  be  based 
upon  the  number  of  occupants.  It  sometimes  happens,  however, 
that  this  information  is  not  available,  or  the  character  of  the  room  is 
such  that  the  number  of  persons  occupying  it  may  vary,  as  in  the  case 
of  public  waiting  rooms,  toilet  rooms,  etc.  In  instances  of  this  kind, 
the  required  air-volume  may  be  based  upon  the  number  of  changes 
per  hour.  In  using  this  method,  various  considerations  must  be  taken 
into  account,  such  as  the  use  of  the  room  and  its  condition  as  to  crowd- 
ing, character  of  occupants,  etc.  In  general,  the  following  will  be 
found  satisfactory  for  average  conditions : 


206 


HEATING  AND  VENTILATION 


11 


TABLE  IV 
Number  of  Changes  of  Air  Required  in  Various  Rooms 


USE  or  ROOM 

CHANGES  OF  AIR  PER  HOUR 

Public  Waiting  Room 

4  to  5 

Public  Toilets 

5 

6 

Coat  and  Locker  Rooms 

4 

5 

Museums 

3 

4 

Offices,  Public 

4 

5 

Offices,  Private 

3 

4 

Public  Dining  Rooms 

4 

5 

Living  Rooms 

3 

4 

Libraries,  Public 

4 

5 

Libraries,  Private 

3 

4 

Force  for  Moving  Air.  Air  is  moved  for  ventilating  purposes  in 
two  ways:  (1)  by  expansion  due  to  heating;  (2)  by  mechanical  means. 
The  effect  of  heat  on  the  air  is  to  increase  its  volume  and  therefore 
lessen  its  density  or  weight,  so  that  it  tends  to  rise  and  is  replaced  by 
the  colder  air  below.  The  available  force  for  moving  air  obtained  in 
this  way  is  very  small,  and  is  quite  likely  to  be  overcome  by  wind  or 
external  causes.  It  will  be  found  in  general  that  the  heat  used  for 
producing  velocity  in  this  manner,  when  transformed  into  work  in 
the  steam  engine,  is  greatly  in 
excess  of  that  required  to  pro- 
duce the  same  effect  by  the  use  of 
a  fan. 

Ventilation  by  mechanical 
means  is  performed  either  'by 
pressure  or  by  suction.  The  for- 
mer is  used  for  delivering  fresh  air 
into  a  building,  and  the  latter  for 
removing  the  foul  air  from  it. 
By  both  processes  the  air  is  moved 
without  change  in  temperature, 
and  the  force  for  moving  must  be  sufficient  to  overcome  the  effects 
of  wind  or  changes  in  outside  temperature.  Some  form  of  fan  is  used 
for  this  purpose. 

Measurements  of  Velocity.  The  velocity  of  air  in  ventilating 
ducts  and  flues  is  measured  directly  by  an  instrument  called  an  ane- 
mometer. A  common  form  of  this  instrument  is  shown  in  Fig.  1.  It 
consists  of  a  series  of  flat  vanes  attached  to  an  axis,  and  a  series  of  dials. 


Fig.  1.    Common  Form  of  Anemometer,  for 
Measuring  Velocity  of  Air-Currents. 


207 


12  HEATING  AND  VENTILATION 


The  revolution  of  the  axis  causes  motion  of  the  hands  in  proportion  to 
the  velocity  of  the  air,  and  the  result  can  he  read  directly  from  the  dials 
for  any  given  period. 

For  approximate  results  the  anemometer  may  be  slowly  moved 
across  the  opening  in  either  vertical  or  horizontal  parallel  lines,  so 
that  the  readings  will  be  made  up  of  velocities  taken  from  all  parts  of 
the  opening.  For  more  accurate  work,  the  opening  should  be  divided 
into  a  number  of  squares  by  means  of  small  twine,  and  readings  taken 
at  the  center  of  each.  The  mean  of  these  readings  will  give  the 
average  velocity  of  the  air  through  the  entire  opening. 

AIR  DISTRIBUTION 

The  location  of  the  air  inlet  to  a  room  depends  upon  the  size  of 
the  room  and  the  purpose  for  which  it  is  used.  In  the  case  of  living 
rooms  in  dwelling-houses,  the  registers  are  placed  either  in  the  floor 
or  in  the  wall  near  the  floor;  this  brings  the  warm  air  in  at  the  coldest 
part  of  the  room  and  gives  an  opportunity  for  warming  or  drying  the 
feet  if  desired.  In  the  case  of  schoolrooms,  where  large  volumes  of 
warm  air  at  moderate  temperatures  are  required,  it  is  best  to  discharge 
it  through  openings  in  the  wall  at  a  height  of  7  or  3  feet  from  the  floor; 
this  gives  a  more  even  distribution,  as  the  warmer  air  tends  to  rise  and 
hence  spreads  uniformly  under  the  ceiling;  it  then  gradually  displaces 
other  air,  and  the  room  becomes  filled  with  pure  air  without  sensible 
currents  or  drafts.  The  cooler  air  sinks  to  the  bottom  of  the  room,  and 
can  be  taken  off  through  ventilating  registers  placed  near  the  floor. 
The  relative  positions  of  the  inlet  and  outlet  are  often  governed  to 
some  extent  by  the  building  construction;  but,  if  possible,  they  should 
both  l>e  located  in  the  same  side  of  the  room.  Figs.  2,  3,  and  4  show 
common  arrangements. 

The  vent  outlet  should  always,  if  possible,  be  placed  in  an  inside 
wall ;  otherwise  it  will  become  chilled  and  the  air-flow  through  it  will 
become  sluggish.  In  theaters  and  churches  which  are  closely  packed, 
the  air  should  enter  at  or  near  the  floor,  in  finely-divided  streams;  and 
the  discharge  ventilation  should  be  through  openings  in  the  ceiling. 
The  reason  for  this  is  the  large  amount  of  animal  heat  given  off  from 
the  bodies  of  the  audience;  this  causes  the  air  to  become  still  further 
heated  after  entering  the  room,  and  the  tendency  is  to  rise  continuously 


ROh 


HEATING  AND  VENTILATION 


13 


from  floor  to  ceiling,  thus  carrying  away  all  impurities  from  respiration 
as  fast  as  they  are  given  off. 

All  audience  halls  in  which  the  occupants  are  closely  seated  should 
be  treated  in  the  same  manner,  when  possible.  This,  however,  can- 
not always  be  done,  as  the  seats  are  often  made  removable  so  that  the 


ours/oe  WALL 


OUTSIDE  \MALL 


OUTSIDE  V&UJ. 


Fig.  3.  Fig.  3.  Fig.  4. 

Diagrams  Showing  Relative  Positions  of  Air  Inlets  and  Outlets  as  Commonly.  Arranged. 

floor  can  be  used  for  other  purposes.  In  cases  of  this  kind,  part  of 
the  air  may  be  introduced  through  floor  registers  placed  along  the  outer 
aisles,  and  the  remainder  by  means  of  wall  inlets  the  same  as  for  school- 
rooms. The  discharge  ventilation  should  be  partly  through  registers 
near  the  floor,  supplemented  by  ample  ceiling  vents  for  use  when  the 
hall  is  crowded  or  the  outside  temperature  high. 

The  matter  of  air-velocities,  size  of  flues,  etc.,  will  be  taken  up 
under  the  head  of  "Indirect  Heating." 

HEAT  LOSS  FROM  BUILDINGS 

A  British  Thermal  Unit,  or  B.  T.  U.,  has  been  defined  as  the 
amount  of  heat  required  to  raise  the  temperature  of  one  pound  of 
water  one  degree  F.  This  measure  of  heat  enters  into  many  of  the 
calculations  involved  in  the  solving  of  problems  in  heating  and  ventila- 
tion, and  one  should  familiarize  himself  with  the  exact  meaning  of 
the  term. 

Causes  of  Heat  Loss.  The  heat  loss  from  a  building  is  due  to 
the  following  causes:  (1)  radiation  and  conduction  of  heat  through 
walls  and  windows;  (2)  leakage  of  warm  air  around  doors  and  win- 
dows and  through  the  walls  themselves;  and  (3)  heat  required  to  warm 
the  air  for  ventilation. 

Loss  through  Walls  and  Windows.  The  loss  of  heat  through 
the  walls  of  a  building  depends  upon  the  material  used  in  construction 


1 1 


HEATING  AND  VENTILATION 


TABLE  V 

Heat  Losses  in  B.  T.  U.  per  Square  Foot  of  Surface  per  Hour- 
Southern  Exposure 


IDE 

AND 

OUT- 

10° 

20° 

30° 

40° 

50°    60° 

70° 

80° 

90° 

100° 

8-in.  Br  ck  Wall  

5 

9 

13 

18 

22    27    31 

36    40 

45 

12-in.  Br  ck  Wall  

4 

7 

10        13 

ie;  20  23 

26 

30    33 

16-in.  Br  ck  Wall  

3 

5 

8     ;  10 

13    16 

19 

22 

24 

27 

20-in.  Br  ck  Wall  

2.8 

4.5 

7          9 

11     14 

16 

18 

20 

23 

24-in.  Br  ck  Wall  

2.5 

4 

6 

8 

10    12 

14 

1(1 

18 

20 

2S-in.  Brick  Wall  

2 

3.5 

5 

7 

9    11 

13 

14 

16 

18 

32-in.  Brick  Wall  

1    5 

3 

4  5 

fi 

8    10 

11 

13 

15 

16 

Single  Window  

12 

24 

36 

•lit 

60    73 

85 

93110122 

Double  Window  

8 

16 

24 

32 

40   48 

56 

62 

7D 

78 

Single  Skylight  

11 

21 

31 

42    52    63 

73 

84 

94 

104 

Double  Skylight  

7 

14 

90 

28    35 

1" 

48 

56 

62 

70 

12 

16    20 

94 

98 

•» 

Ofi 

•3 

K 

Q 

i  - 

90 

')•-> 

2-in.  Solid  Plaster  Partition  

6 

12 

18 

24    30 

36 

•  4? 

48 

54 

60 

3-in.  Solid  Plaster  Partition  5 

10 

15 

20!   25 

30s  35 

41 

45 

50 

Concrete  Floor  on  Brick  Arch.  ...       9        4 

6.5 

9|   11 

13)   15 

18 

20    22 

Wood  Floor  on  Brick  Arch  

1.5    3 

4   5 

6:      7 

9    10 

12    13    15 

Double  Wood  Floor  

1 

2 

3 

4      5 

6 

7 

8      9    10 

Walls  of  Ordinary  Wooden 

Dwellings  

3        5 

8 

10,   13 

16    19 

22    24    27 

1        ;        i 

For  solid  stone  walls,  multiply  the  figures  for  brick  of  the  same  thickness 
by  1.7.  Where  rooms  have  a  cold  attic  above  or  cellar  beneath,  multiply  the 
heat  loss  through  walls  and  windows  by  1.1. 

Correction  for  Leakage.  The  figures  given  in  the  above  table  apply  only 
to  the  most  thorough  construction.  For  the  average  well-built  house,  the 
results  should  be  increased  about  10  per  cent;  for  fairly  good  construction, 
20  per  cent;  and  for  poor  construction,  30  per  cent. 

Table  V  applies  only  to  a  southern  exposure;  for  other  exposures  multi- 
ply the  heat  loss  given  in  Table  V  by  the  factors  given  in  Table  VI. 

of  the  wall,  the  thickness,  the  number  of  layers,  and  the  difference 
between  the  inside  and  outside  temperatures.  The  exact  amount  of 
heat  lost  in  this  way  is  very  difficult  to  determine  theoretically,  hence 
we  depend  principally  on  the  results  of  experiments. 

Loss  by  Air-Leakage.  The  leakage  of  air  from  a  room  varies 
from  one  to  two  or  more  changes  of  the  entire  contents  per  hour, 
depending  upon  the  construction,  opening  of  doors,  etc.  It  is  com- 
mon practice  to  allow  for  one  change  per  hour  in  well-constructed 
buildings  where  two  walls  of  the  room  have  an  outside  exposure.  As 
the  amount  of  leakage  depends  upon  the  extent  of  exposed  wall  and 
window  surface,  the  simplest  way  of  providing  for  this  is  to  increase 


310 


HEATING  AND  VENTILATION  15 

TABLE  VI 
Factors  for  Calculating  Heat  Loss  for  Other  than  Southern  Exposures 


EXPOSURE 

FACTOR 

N. 

1.32 

E. 

1.12 

S. 

1.0 

w. 

1.20 

N.E. 

1.22 

N.W. 

1.26 

S.E. 

1.06 

s.w. 

1.10 

N.,  E.,  S.,  and  W.,  or  total  exposure 

1.16 

the  total  loss  through  walls  and  windows  by  a  factor  depending  upon 
the  tightness  of  the  building  construction.  Authorities  differ  con- 
siderably in  the  factors  given  for  heat  losses,  and  there  are  various 
methods  for  computing  the  same.  The  figures  given  in  Table  V  have 
been  used  extensively  in  actual  practice,  and  have  been  found  to  give 
good  results  when  used  with  judgment.  The  table  gives  the  heat  losses 
through  different  thicknesses  of  walls,  doors,  windows,  etc.,  in  B.  T. 
IL,  per  square  foot  of  surface  per  hour,  for  varying  differences  in  inside 
and  outside  temperatures. 

In  computing  the  heat  loss  through  walls,  only  those  exposed  to 
the  outside  air  are  considered. 

In  order  to  make  the  use  of  the  table  clear,  we  shall  give  a  num- 
ber of  examples  illustrating  its  use: 

Example  1.  Assuming  an  inside  temperature  of  70°,  what  will  be  the 
heat  loss  from  a  room  having  an  exposed  wall  surface  of  200  square  feet  and  a 
gclass  surface  of  50  square  feet,  when  the  outside  temperature  is  zero?  The 
wall  is  of  brick,  16  inches  in  thickness,  and  has  a  southern  exposure;  the  win- 
dows are  single;  and  the  construction  is  of  the  best,  so  that  no  account  need 
be  taken  of  leakage 

We  find  from  Table  V,  that  the  factor  for  a  16-inch  brick  wall 
with  a  difference  in  temperature  of  70°  is  19,  and  that  for  glass  (single 
window)  under  the  same  condition  is  85;  therefore, 

Loss  through  walls          =  200  X   19  =   3,800 
Loss  through  windows  =    .  50  X  85    =   4,250 

Total  loss  per  hour  =   8,050  B.T.U. 

Example  2.  A  room  15  ft.  square  and  10  ft.  high  has  two  exposed  walls, 
one  toward  the  north,  and  the  other  toward  the  west.  There  are  4  windows, 
each  3  feet  by  6  feet  in  size.  The  two  in  the  north  wall  are  double,  while  the 


311 


16  HEATING  AND  VENTILATION 


other  two  are  single.  The  walls  are  of  brick,  20  inches  in  thickness.  With  an 
inside  temperature  of  70°.  what  will  be  the  heat  loss  per  hour  when  it  is  10° 
below  zero? 

Total  exposed  surfaee  =  15  X  10  X  2  -  300 
Glass  surface  =    3  X    C  X  4  =     72 

Net  wall  surface  228 

Difference  between  inside  and  outside  temperature  SO0. 
Factor  for  20-inch  brick  wall  is  18. 
Factor  for  single  window  is  93. 
Factor  for  double  window  is  62. 
The  heat  losses  are  as  follows: 

Wall,  228  X  18  -  4,104 

Single  windows,     36  X  93  =  3,348 

Double  windows,   36  X  62  =  2,232 


9,684  B.T.U. 

As  one  side  is  toward  the  north,  and  the  other  toward  the  west,  the 
actual  exposure  is  N.  W.    Looking  in  Table  VI,  we  find  the  correction 
factor  for  this  exposure  to  be  1.26;  therefore  the  total  heat  loss  is 
9,684  X  1.26  =  12,201.84 B.T.U. 

1'lxnmple  3.  A  dwelling-house  of  fair  wooden  construction  measures 
160  ft.  around  the  outside;  it  has  2  stories,  each  8  ft.  in  height;  the  windows 
are  single,  and  the  glass  surface  amounts  to  one-fifth  the  total  exposure;  the 
attic  and  cellar  are  umvarmed.  If  8,000  B.  T.  I*,  are  utilized  from  each  pound 
of  coal  burned  in  the  furnace,  how  many  pounds  will  be  required  per  hour  to 
maintain  a  temperature  of  70°  when  it  is  20°  above  zero  outside? 

Total  exposure  =     160  X  1 
Glass  surface     =  2,560  -H 


Net  wall 

Temperature  difference  =  70  —  20  =  50° 
Wall  2,048  X  13    =  26,624 

Glass  512  X  60    =  30,720 


57,344  B.T.U. 

As  the  building  is  exposed  on  all  sides,  the  factor  for  exposure  will  be 
the  average  of  those  for  N.,  E.,  S.,  and  W.,  or 

(1.32  +  1.12  +  1.0  +  1.20)  -f-  4  =  1  16 
The  house  has  a  cold  cellar  and  attic,  so  we  must  increase  the  heat  loss 


318 


HEATING  AND  VENTILATION  17 

10  per  cent  for  each  of  the  first  two  conditions,  and  20  per  cent  for  the 
last.     Making  these  corrections  we  have: 

57,344  X  1.16  X  1.10  X  1.10  X  1.20  =  96,338  B.T.U. 
If  one  pound  of  coal  furnishes  8,000  B.  T.  IL,  then  96,338  -f-  8,000  = 
12  pounds   of  coal  per  hour  required  to  warm  the  building  to  70° 
under  the  conditions  stated. 

Approximate  Method.  For  dwelling-houses  of  the  average  con- 
struction, the  following  simple  method  for  calculating  the  heat  loss 
may  be  used.  Multiply  the  total  exposed  surface  by  45,  which  will 
give  the  heat  loss  in  B.  T.  U.  per  hour  for  an  inside  temperature  of  70° 
in  zero  weather. 

This  factor  is  obtained  in  the  following  manner :  Assume  the  glass 
surface  to  be  one-sixth  the  total  exposure,  which  is  an  average  propor- 
tion. Then  each  square  foot  of  exposed  surface  consists  one-sixth 
of  glass  and  five-sixths  of  wall,  and  the  heat  loss  for  70°  difference  in 
temperature  would  be  as  follows : 

Wall  —  X  19  =  15.8 

Glass  —  X  85  =  14.1 
8 

29.9 

Increasing  this  20  per  cent  for  leakage,  16  per  cent  for  exposure,  and 
10  per  cent  for  cold  ceilings,  we  have : 

29.9  X  1.20  X  1.16  X  1.10  =  45. 

The  loss  through  floors  is  considered  as  being  offset  by  including 
the  kitchen  walls  of  a  dwelling-house,  which  are  warmed  by  the  range, 
and  which  would  .not  otherwise  be  included  if  computing  the  size  of  a 
furnace  or  boiler  for  heating.  . 

If  the  heat  loss  is  required  for  outside  temperatures  other  than 
zero,  multiply  by  50  for  10  degrees  below,  and  by  40  for  10  degrees 
above  zero. 

This  method  is  convenient  for  approximations  in  the  case  of 
dwelling-houses;  but  the  more  exact  method  should  be  used  for  other 
types  of  buildings,  and  in  all  cases  for  computing  the  heating  surface 
for  separate  rooms.  When  calculating  the  heat  loss  from  isolated 
rooms,  the  cold  inside  walls  as  well  as  the  outside  must  be  considered. 

The  loss  through  a  wall  next  to  a  cold  attic  or  other  un  warmed  space 
may  in  general  be  taken  as  about  two-thirds  that  of  an  outside  wall. 


18  HEATING  AND  VENTILATION 


Heat  Loss  by  Ventilation.  One  B.  T.  U.  will  raise  the  tempera- 
ture of  1  cubic-  foot  of  air  55  degrees  at  average  temperatures  and 
pressures,  or  will  raise  55  cubic  feet  1  degree,  so  that  the  heat  required 
for  the  ventilation  of  any  room  can  be  found  by  the  following  formula : 

Cu.  ft.  of  air  per  hour   X   Number  of  degrees  rise 

^  =    B.  1 .  I  .  required. 

To  compute  the  heat  loss  for  any  given  room  which  is  to  be 
ventilated,  first  find  the  loss  through  walls  and  windows,  and  correct 
for  exposure  and  leakage;  then  compute  the  amount  required  for 
ventilation  as  above,  and  take  the  sum  of  the  two.  An  inside  tem- 
perature of  70°  is  always  assumed  unless  otherwise  stated. 

Examples.  What  quantity  of  heat  will  be  required  to  warm  100,000 
cubic  feet  of  air  to  70°  for  ventilating  purposes  when  the  outside  temperature 
is  10  below  zero? 

100,000  X  80  -r-  55  =  145,454  B.  T.  U. 

How  many  B.  T.  T  .  will  be  required  per  hour  for  the  ventilation  of  a 
church  seating  500  people,  in  zero  weather? 

Referring  to  Table  III,  we  find  that  the  total  air  required  per 
hour  is  1,200  X  500  -  600,000  cu.  ft.;  therefore  600,000  X  70  -T-  55 
-  763,636  B.  T.  U. 

Rise  in  Temperature  . 
The  factor  —         — — —  -    is  approximately  1.1  for  60  , 

1.3  for  70°,  and  1.5  for  80°.  Assuming  a  temperature  of  70°  for  the 
entering  air,  we  may  multiply  the  air-volume  supplied  for  ventilation 
by  1.1  for  an  outside  temperature  of  10°  above  0,  by  1.3  for  zero,  and 
by  1 .5  for  10°  below  zero — which  covers  the  conditions  most  commonly 
met  with  in  practice. 

EXAMPLES  FOR  PRACTICE 

1.  A  room  in  a  grammar  school  28  ft.  by  32  ft.  and  12  feet  high  is 
to  accommodate  50  pupils.     The  walls  are  of  brick  16  inches  in  thick- 
ness; and  there  are  6  single  windows  in  the  room,  each  3  ft.  by  6  ft.; 
there  are  warm  rooms  above  and  below;  the  exposure  is  S.  E.     How 
many  B.  T.  U.  will  be  required  per  hour  for  warming  the  room,  and 
how  many  for  ventilation,  in  zero  weather,  assuming  the  building  to 
be  of  average  construction? 

Axs.      24,261  +  for  warming;  152,727  +  for  ventilation. 

2.  A  stone  church  seating  400  people  has  walls  20  inches  in 
thickness.     It  has  a  wall  exposure  of  5,000  square  feet,  a  glass  expos- 


814 


HEATING  AND  VENTILATION  19 

tire  (single  windows)  of  600  square  feet,  and  a  roof  exposure  of  7,000 
square  feet;  the  roof  is  of  2-inch  pine  plank,  and  the  factor  for  heat 
loss  may  be  taken  the  same  as  for  a  2-inch  wooden  door.  The  floor 
is  of  wood  on  brick  arches,  and  has  a.n  area  of  4,000  square  feet.  The 
building  is  exposed  on  all  sides,  and  is  of  first-class  construction. 
What  will  be  the  heat  required  per  hour  for  both  warming  and  ventila- 
tion when  the  outside  temperature  is  20°  above  zero? 

ANS.     296,380  for  warming;  436,363  +  for  ventilation. 
3.     A  dwelling-house  of  average  wooden  construction  measures 
200  feet  around  the  outside,  and  has  3  stories,  each  9   feet   high. 
Compute  the  heat  loss  by  the  approximate  method  when  the  tem- 
perature is  10°  below  zero. 

ANS.     270,000  B.  T.  U.  per  hour. 

FURNACE  HEATING 

In  construction,  a  furnace  is  a  large  stove  with  a  combustion 
chamber  of  ample  size  over  the  fire,  the  whole  being  inclosed  in  a 
casing  of  sheet  iron  or  brick.  The  bottom  of  the  casing  is  provided 
with  a  cold-air  inlet,  and  at  the  top  are  pipes  which  connect  with 
registers  placed  in  the  various  rooms  to  be  heated.  Cold,  fresh  air 
is  brought  from  out  of  doors  through  a  pipe  or  duct  called  the  cold-air 
box;  this  air  enters  the  space  between  the  casing  and  the  furnace  near 
the  bottom,  and,  in  passing  over  the  hot  surfaces  of  the  fire-pot  and 
combustion  chamber,  becomes  heated.  It  then  rises  through  the 
warm-air  pipes  at  the  top  of  the  casing,  and  is  discharged  through  the 
.registers  into  the  rooms  above.  / 

As  the  warm  air  is  taken  from  the  top  of  the  furnace,  cold  air 
flows  in  through  the  cold-air  box  to  take  its  place.  The  air  for  heating 
the  rooms  does  not  enter  the  combustion  chamber. 

Fig.  5  shows  the  general  arrangement  of  a  furnace  with  its  con- 
necting pipes.  The  cold-air  inlet  is  seen  at  the  bottom,  and  the  hot-air 
pipes  at  the  top;  these  are  all  provided  with  dampers  for  shutting  off  or 
regulating  the  amount  of  air  flowing  through  them.  The  feed  or  fire 
door  is  shown  at  the  front,  and  the  ash  door  beneath  it;  a  water-pan  is 
placed  inside  the  casing,  and  furnishes  moisture  to  the  warm  air  before 
passing  into  the  rooms;  water  is  either  poured  into  the  pan  through  an 
opening  in  the  front,  provided  for  this  purpose,  or  is  supplied  auto- 
matically through  a  pipe. 


215 


20 


HEATING  AND  VENTILATION 


The  fire1  is  regulated  by  means  of  a  draft  slide  in  the  ash  door,  and 
a  cold-air  or  regulating  damper  placed  in  the  smoke-pipe.  Clean-out 
doors  are  placed  at  different  points  in  the  casing  for  the  removal  of 


ashes  and  soot.     Furnaces* are  made  either  of  cast  iron,  or  of  wrought- 
iron  plates  riveted  together  and  provided  with  brick-lined  firepots. 

Types  of  Furnaces.     Furnaces  may  be  divided  into  two  general 


216 


HEATING  AND  VENTILATION 


21 


types  known  as  direct-draft  and  indirect-draft.  Fig.  6  shows  a  com- 
mon form  of  direct-draft  furnace  with  a  brick  setting;  the  better  class 
have  a  radiator,  generally  placed  at  the  top,  through  which  the  gases 
pass  before  reaching  the  smoke-pipe.  They  have  but  one  damper, 
usually  combined  with  a  cold-air  check.  Many  of  the  cheaper  direct- 


Fig.  6.    A  Common  Type  of  Direct-Draft  Furnace  in  Brick  Setting. 
'Cast-Iron  Radiator  at  Top. 

draft  furnaces  have  no  radiator  at  all,  the  gases  passing  directly  into 
the  smoke-pipe  and  carrying  away  much  heat  that  should  be  utilized. 

The  furnace  shown  in  Fig.  6  is  made  of  cast  iron  and  has  a  large 
radiator  at  the  top;  the  smoke  connection  is  shown  at  the  rear. 

Fig.  7  represents  another  form  of  direct-draft  furnace.  In  this 
case  the  radiator  is  made  of  sheet-steel  plates  riveted  together,  and  the 
outer  casing  is  of  heavy  galvanized  iron  instead  of  brick. 

In  the  ordinary  indirect-draft  type  of  furnace  (see  Fig.  8),  the 
gases  pass  downward  through  flues  to  a  radiator  located  near  the  base, 


217 


•>•> 


HEATING  AND  VENTILATION 


thence  upward  through  another  flue  to  the  smoke-pipe.  In  addition 
to  the  damper  in  the  smoke-pipe,  a  direct-draft  damper  is  required 
to  give  direct  connection  with  the  funnel  when  coal  is  first  put  on,  to 
facilitate  the  escape  of  gas  to  the  chimney.  When  the  chimney  draft 


r.  7.    Direct-Draft  Furnace  with  Galvanized-Iron  Casing.    Radiator  (at  top) 
Made  of  Riveted  Steel  Plates. 

is  weak,  trouble  from  gas  is  more  likely  to  be  experienced  with  fur- 
naces of  this  type  than  with  those  having  a  direct  draft. 

Grates.  No  part  of  a  furnace  is  of  more  importance  than  the 
grates.  The  plain  grate  rotating  about  a  center  pin  was  for  a  long 
time  the  one  most  commonly  used.  These  grates  were  usually  pro- 
vided with  a  clinker  door  for  removing  any  refuse  too  large  to  pass 
between  the  grate  bars.  The  action  of  such  grates  tends  to  leave  a 


21S 


CONE    EXHAUST    FAN,    INLET    SIDE. 

American  Blower  Co. 


HEATING  AND  VENTILATION 


23 


cone  of  ashes  in  the  center  of  the  fire  causing  it  to  burn  more  freely 
around  the  edges.  A  better  form  of  grate  is  the  revolving  triangular 
pattern,  which  is  now  used  in  many  of  the  leading  furnaces.  It  con- 
sists of  a  series  of  triangular  bars  having  teeth.  The  bars  are  con- 
nected by  gears,  and  are  turned  by  means  of  a  detachable  lever.  If 


Fig.  8.    Indirect-Draft  Tj 


>e  of  Furnace.    Gases  Pass  Downward  to  Kadiator  at  Bottom, 
Thence  Upward  to  Smoke-Pipe.  • 


properly  used,  this  grate  will  cut  a  slice  of  ashes  and  clinkers  from 
under  the  entire  fire  with  little,  if  any  loss  of  uncr  nsumed  coal. 

The  Firepot.  Firepots  are  generally  made  of  cast  iron  or  of  steel 
plate  lined  with  firebrick.  The  depth  ranges  from  about  12  to  18 
inches.  In  cast-iron  furnaces  of  the  better  class,  the  firepot  is  made 
very  heavy,  to  insure  durability  and  to  render  it  less  likely  to  become 
red-hot.  The  firepot  is  sometimes  made  in  two  pieces,  to  reduce  the 


219 


HEATING  AXD  VENTILATION 


liability  to  cracking.  The  heating  surface  is  sometimes  increased  by 
corrugations,  pins,  or  ribs. 

A  tirebrick  lining  is  necessary  in  a  wrought-iron  or  steel  furnace 
to  protect  the  thin  shell  from  the  intense  heat  of  the  fire.  Since  brick- 
lined  rirepots  are  much  less  effective  than  cast-iron  in  transmitting 
heat,  such  furnaces  depend  to  a  great  extent  for  their  efficiency  on  the 
heating  surface  in  the  dora:  and  radiator:  and  this,  as  a  rule,  is  much 
greater  than  in  those  of  cast  iron. 

Cast-iron  furnaces  have  the  advantage  when  coal  is  first  put  on 
ami  the  drop  flues  and  radiator  are  cut  out  by  the  direct  dampen  of 
still  giving  off  heat  'rom  the  fi repot,  while  in  the  case  of  brick  linings 
very  little  heat  is  given  off  5:.  this  way.  and  the  rooms  are  likely  tc 
:.«-"ine  somewhat  cooled  before  the  fresh  coal  becomes  thoroughly 
united. 

Combustion  Chamber.  The  body  of  the  furnace  alx>ve  the  fire- 
ixit.  commonly  called  the  dome  or  feed  section,  provides  a  combustion 
chamlier.  This  chaml>er  should  be  of  sufficient  size  to  permit  the 
i-ases  to  become  thoroughly  mixed  with  the  air  passing  up  through  the 
rire  or  entering  through  openings  provided  for  the  purpose  in  the  feed 
door.  In  a  well-designed  furnace,  this  space  should  be  somewhat 
larger  than  the  firepot. 

Radiator.  The  radiator,  so  called,  with  which  all  furnaces  of 
the  better  class  are  provided,  acts  as  a  sort  of  reservoir  in  which  the 
u'ases  are  kept  in  contact  with  the  air  passing  over  the  furnace  until 
they  have  parted  with  a  considerable  portion  of  their  heat.  Radiators 
an-  built  of  ca-t  iron,  of  steel  plate,  or  of  a  combination  of  the  two. 
The  former  is  more  durable  and  can  l>e  marie  with  fewer  joints,  but 
owing  to  the  difficulty  of  casting  radiators  of  large  size,  steel  plate  is 
commonly  used  for  the  sides. 

The  effectiveness  of  a  radiator  depends  on  its  form,  its  heating 
surface,  and  the  difference  between  the  temperature  of  the  gases  and 
the  surrounding  air.  Owing  to  the  accumulation  of  soot,  the  bottom 
surface  becomes  practically  worthless  after  the  furnace  has  been  in 
•:>e  a  short  time:  surfaces,  to  be  effective,  must  therefore  be  self- 
cleaning. 

If  the  radiator  is  placed  near  the  bottom  of  the  furnace  the  gases 
are  surrounded  by  air  at  the  lowest  temperature,  which  renders  the 
radiator  more  effective  for  a  given  size  than  if  placed  near  the  top  and 


220 


HEATIXG  AXD  VENTILATIOK  2-5 

surrounded  by  warm  air.  On  the  other  hand,  the  cold  air  has  a  ten- 
dency to  condense  the  gases,  and  the  acids  thus  formed  are  likely  to 
corrode  the  iron. 

Heating  Surface.  The  different  heating  surfaces  may  be  de- 
scribed as  follows:  Firepot  surface;  surfaces  acted  upon  by  direct 
rays  of  heat  from  the  fire,  such  as  the  dome  or  combustion  chamber; 
gas-  or  smoke-heated  surfaces,  such  as  flues  or  radiators;  and  ex- 
tended surfaces,  such  as  pins  or  ribs.  Surfaces  unlike  in  character 
and  location,  vary  greatly  in  heating  power,  so  that,  in  making  com- 
parisons of  different  furnaces,  we  must  know  the  kind,  form,  and 
location  of  the  heating  surfaces,  as  well  as  the  area. 

In  some  furnaces  having  an  unusually  large  amount  of  surface, 
it  will  be  -found  on  inspection  that  a  large  part  would  soon  become 
practically  useless  from  the  accumulation  cf  soot.  In  others  a  large 
portion  of  the  surface  is  lined  with  firebrick,  or  is  so  situated  that  the 
air-currents  are  not  likely  to  strike  it. 

The  ratio  of  grate  to  heating  surface  varies  somewhat  according 
to  the  size  of  furnace.  It  may  be  taken  as  1  to  25  in  the  smaller  sizes, 
and  1  to  15  in  the  larger. 

Efficiency.  One  of  the  first  items  to  be  determined  in  esti- 
mating the  heating  capacity  of  a  furnace,  is  its  efficiency — that  is, 
the  proportion  of  the  heat  in  the  coal  that  may  be  utilized  for  warming. 
The  efficiency  depends  chiefly  on  the  area  of  the  heating  surface  as 
compared  with  the  grate,  on  its  character  and  arrangement,  and  on 
the  rate  of  combustion.  The  usual  proportions  between  grate  and 
heating  surface  have  been  stated.  The  rate  of  combustion  required 
to  maintain  a  temperature  of  70°  in  the  house,  depends,  of  course, 
on  the  outside  temperature.  In  very  cold  weather  a  rate  of  4  to  5 
pounds  of  coal  per  square  foot  of  grate  per  hour  must  be  main- 
tained. 

One  pound  of  good  anthracite  coal  will  give  off  about  13,000 
B.  T.  U.,  and  a  good  furnace  should  utilize  70  per  cent  of  this  heat. 
The  efficiency  of  an  ordinary  furnace  is  often  much  less,  sometimes 
as  low  as  50  per  cent. 

In  estimating  the  required  size  of  a  first-class  furnace  with  good 
chimney  draft,  we  may  safely  count  upon  a  maximum  combustion 
of  5  pounds  of  coal  per  square  foot  of  grate  per  hour,  and  may  assume 
that  8,000  B.  T.  U.  will  be  utilized  for  warming  purposes  from  each 


221 


20  HEATING  AND  VENTILATION 


pound  burned.     This  quantity  corresponds  to  an  efficiency  of  GO 

per  cent. 

Heating  Capacity.  Having  determined  the  heat  loss  from  a 
building  by  the  methods  previously  given,  it  is  a  simple  matter  to 
compute  the  size  of  grate  necessary  to  burn  a  sufficient  quantity  of 
coal  to  furnish  the  amount  of  heat  required  for  warming. 

In  computing  the  size  of  furnace,  it  is  customary  to  consider  the 
whole  house  as  a  single  room,  with  four  outside  walls  and  a  cold  attic. 
The  heat  losses  by  conduction  and  leakage  are  computed,  and  in- 
creased 10  per  cent  for  the  cold  attic,  and  16  per  cent  for  exposure. 
The  heat  delivered  to  the  various  rooms  may  be  considered  as  being 
made  up  of  two  parts — first,  that  required  to  warm  the  outside  air 
up  to  70°  (the  temperature  of  the  rooms);  and  second,  the  quantity 
which  must  be  added  to  this  to  offset  the  loss  by  conduction  and  leak- 
age. Air  is  usually  delivered  through  the  registers  at  a  temperature 
of  120°,  with  zero  conditions  outside,  in  the  best  class  of  residence 

work;  so  that  —  —  of  the  heat  given  to  the  entering  air  may  be  con- 

50 
sidered  as  making. up  the  first  part,  mentioned  above,  leaving— — 

available  for  purely  heating  purposes.     From  ihis  it  is  evident  that 

50 
the  heat  supplied  to  the  entering  air  must  be  equal  to  1    -f-  -  =  2.4 

times  that  required  to  offset  the  loss  by  conduction  and  leakage. 

Example.  The  loss  through  the  walls  and  windows  of  a  building  is 
found  to  be  80,000  B.  T.  U.  per  hour  in  zero  weather.  What  will  be  the  size 
of  furnace  required  to  maintain  an  inside  temperature  of  70  degrees? 

From  the  above,  we  have  the  total  heat  required,  equal  to  80,000 
X  2.4  =  192,000  B.  T.  U.  per  hour.  If  we  assume  that  8,000  B.  T. 
U.  are  utilized  per  pound  of  coal,  then  192,000  •*•  8,000  -  24  pounds 
of  coal  required  per  hour;  and  if  o  pounds  can  be  burned  on  each 

24 
square  foot  of  grate  per  hour,  then-^-  ==  4.8   square  feet  required. 

A  grate  30  inches  in  diameter  has  an  area  of  4.9  square  feet,  and  is  the 
size  we  should  use. 

When  the  outside  temperature  is  taken  as  10°  below  zero,  multi- 
ply by  2.6  instead  of  2.4;  and  multiply  by  2.8  for  20°  below. 

Table  VII  will  be  found  useful  in  determining  the  diameter  of 
fi repot  required. 


HEATING  AND  VENTILATION"  27 


TABLE  VII 

Firepot  Dimensions 

AVERAGE  DIAMETER  OF  GRATE,  IN  INCHES 

AREA  IN  SQUARE  FEET 

18 

1.77 

20 

2.18 

22 

2.64 

24 

3.14 

26 

3.69 

28 

4.27 

30 

4.91 

32 

5.58 

EXAMPLES   FOR   PRACTICE 

1.  A  brick  apartment  house  is  20  feet  wide,  and  has  4  stories, 
each  being  10  feet  in  height.     The  house  is  one  of  a  block,  and  is 
exposed  only  at  the  front  and  rear.     The  walls  are  16  inches  thick, 
and  the  block  is  so  sheltered  that  no  correction  need  be  made  for 
exposure.     Single  windows  make  up  ^  the  total  exposed  surface. 
Figure  for  cold  attic  but  warm  basement.     What  area  of  grate  surface 
will  be  required  for  a  furnace  to  keep  the  house  at  a  temperature  of 
70°  when  it  is  10°  below  zero  outside?  ANS.  3.5  square  feet. 

2.  A  house  having  a  furnace  with  a  firepot  30  inches  in  diameter, 
is  not  sufficiently  warmed,  and  it  is  decided  to  add  a  second  furnace 
to  be  used  in  connection  with  the  one  already  in.     The  heat  loss  from 
the  building  is  found  by  computation  to  be  133,600  B.  T.  U.  per  hour, 
in  zero  weather.     What  diameter  of  firepot  will  be  required  for  the 
extra  furnace?  ANS.  24  inches. 

Location  of  Furnace.  A  furnace  should  be  so  placed  that  the 
warm-air  pipes  will  be  of  nearly  the  same  length.  The  air  travels 
most  readily  through  pipes  leading  toward  the  sheltered  side  of  the 
house  and  to  the  upper  rooms.  Therefore  pipes  leading  towrard  the 
north  or  west,  or  to  rooms  on  the  first  floor,  should  be  favored  in 
regard  to  length  and  size.  The  furnace  should  be  placed  somewhat 
to  the  north  or  west  of  the  center  of  the  house,  or  toward  the  points 
of  compass  from  which  the  prevailing  winds  blow. 

Smoke=Pipes.  Furnace  smoke-pipes  range  in  size  from  about 
6  inches  in  the  smaller  sizes  to  8  or  9  inches  in  the  larger  ones.  They 
are  generally  made  of  galvanized  iron  of  No.  24  gauge  or  heavier. 
The  pipe  should  be  carried  to  the  chimney  as  directly  as  possible, 


323 


28  HEATING  AND  VENTILATION 

avoiding  bends  which  increase  the  resistance  and  diminish  the  draft. 
Where  a  smoke-pipe  passes  through  a  partition,  it  should  be  pro- 
tected by  a  soapstone  or  double-perforated  metal  collar  having  a 
diameter  at  least  8  inches  greater  than  that  of  the  pipe.  The  top  of 
the  smoke-pipe  should  not  be  placed  within  8  inches  of  unprotected 
beams,  nor  less  than  0  inches  under  beams  protected  by  asbestos  or 
plaster  with  a  metal  shield  beneath.  A  collar  to  make  tight  con- 
nection with  the  chimney  should  be  riveted  to  the  pipe  about  5  inches 
from  the  end,  to  prevent  the  pipe  being  pushed  too  far  into  the  flue. 
Where  the  pipe  is  of  unusual  length,  it  is  well  to  cover  it  to  prevent 
loss  of  heat  and  the  condensation  of  smoke. 

Chimney  Flues.  Chimney  flues,  if  built  of  brick,  should  have 
walls  8  inches  in  thickness,  unless  terra-cotta  linings  are  used,  when 
only  4  inches  of  brickwork  is  required.  Except  in  small  houses 
where  an  8  by  8-inch  flue  may  be  used,  the  nominal  size  of  the  smoke 
flue  should  be  at  least  8  by  12-inches;to  allow  for  contractions  or  off- 
sets. A  clean-out  door  should  be  placed  at  the  bottom  of  the  flue, 
for  removing  ashes  and  soot.  A  square  flue  cannot  be  reckoned  at 
its  full  area,  as  the  corners  are  of  little  value.  To  avoid  down  drafts, 
the  top  of  the  chimney  must  be  carried  above  the  highest  point  of  the 
roof  unless  provided  with  a  suitable  hood  or  top. 

Cold=Air  Box.  The  cold-air  box  should  be  large  enough  to 
supply  a  volume  of  air  sufficient  to  fill  all  the  hot-air  pipes  at  the  same 
time.  If  the  supply  is  too  small,  the  distribution  is  sure  to  be  unequal, 
and  the  cellar  will  become  overheated  from  lack  of  air  to  carry  away 
the  heat  generated. 

If  a  box  is  made  too  small,  or  is  throttled  down  so  that  the  volume 
of  air  entering  the  furnace  is  not  large  enough  to  fill  all  the  pipes, 
it  will  be  found  that  those  leading  to  the  less  exposed  side  of  the 
house  or  to  the  upper  rooms  will  take  the  entire  supply,  and  that 
additional  air  to  supply  the  deficiency  will  be  drawn  down  through 
registers  in  rooms  less  favorably  situated.  It  is  common  practice 
to  make  the  area  of  the  cold-air  box  three-fourths  the  combined 
area  of  the  hot-air  pipes.  The  inlet  should  be  placed  where  the 
prevailing  cold  winds  will  blow  into  it;  this  is  commonly  on  the  north 
or  west  side  of  the  house.  If  it  is  placed  on  the  side  awav  from  the 
wind,  warm  air  from  the  furnace  is  likely  to  be  drawn  out  through 
the  cold -air  box. 


224 


HEATING  AND  VENTILATION 


2!) 


Whatever  may  be  the  location  of  the  entrance  to  the  cold-air 
box,  changes  in  the  direction  of  the  wind  may  take  place  which  will 
bring  the  inlet  on  the  wrong  side  of  the  house.  To  prevent  the 
possibility  of  such  changes  affecting  the  action  of  the  furnace,  the 
cold-air  box  is  sometimes  extended  through  the  house  and  left  open 
at  both  ends,  with  check-dampers  arranged  to  prevent  back-drafts. 
These  checks  should  be  placed  some  distance  from  the  entrance,  to 
prevent  their  becoming  clogged  with  snow  or  sleet. 

The  cold-air  box  is  generally  made  of  matched  boards;  but 
galvanized  iron  is  much  better;  it  costs  more  than  wood,  but  is  well 
worth  the  extra  expense  on  account  of  tightness,  which  keeps  the  dust 
and  ashes  from  being  drawn  into  the  furnace  casing  to  be  discharged 
through  the  registers  into  the  rooms  above. 

The  cold-air  inlet  should  be  covered  with  galvanized  wire  netting 
with  a  mesh  of  at  least  three-eighths  of  an  inch.  The  frame  to  which 
it  is  attached  should  not 

^  FOFI  RETURNING 

be  smaller  than  the  in-  |'|  {  AIR  mow  ABOVE 

side  dimensions   of    the 

cold-air  box.     A  door  to 

admit  air  from  the  cellar 

to  the    cold-air    box    is 

generally    provided.     As 

a    rule,    air    should    be 

taken   from  this  source, 

only  when  the  house  is 

temporarily    unoccupied 

or  during  high  winds. 

Return  Duct.  In 
some  cases  it  is  desirable 
to  return  air  to  the  fur- 
nace from  the  rooms 
above,  to  be  reheated.  Ducts  for  this  purpose  are  common  in  places 
where  the  winter  temperature  is  frequently  below  zero.  Return 
ducts  when  used,  should  be  in  addition  to  the  regular  cold-air  box. 
Fig.  9  shows  a  common  method  of  making  the  connection  between 
the  two.  By  proper  adjustment  of  the  swinging  damper,  the  air  can 
be  taken  either  from  out  of  doors  or  through  the  register  from  the 
room  above.  The  return  register  is  often  placed  in  the  hallway  of 


Fig  9.    Common  Method  of  Connecting  Return  Duct  to 
Cold- Air  Box.     • 


30 


HEATING  AND  VENTILATION 


a  house,  •  so  that  it  will  take  the  cold  air  which  rushes  in  when  the 
door  is  opened  and  also  that  which  may  leak  in  around  it  while 
closed.  Check-valves  or  flaps  of  light  gossamer  or  woolen  cloth 
should  be  placed  between  the  cold-air  box  and  the  registers  to  pre- 
vent back-drafts  during  winds. 

The  return  duct  should  not  be  used  too  freely  at  the  expense  of 
outdoor  air,  and  its  use  is  not  recommended  except  during  the  night 
when  air  is  admitted  to  the  sleeping  rooms  through  open  windows. 

Warm=Air  Pipes.  The  required  size  of  the  warm-air  pipe  to 
any  given  room,  depends  on  the  heat  loss  from  the  room  and  on  the 
volume  of  warm  air  required  -to  offset  this  loss.  Each  cubic  foot  of 
air  warmed  from  zero  to  120  degrees  brings  into  a  room  2.2  B.  T.  U. 
\Ve  have  already  seen  that  in  zero  weather,  with  the  air  entering  the 

50 

registers  at  120  degrees,  only    -— -  of  the  heat  contained  in  the  air  is 

available  for  offsetting  the  losses  by  radiation  and  conduction,  so  that 

50 

only  2.2  X    —    ==    .OB.  T.  U.  in  each  cubic  foot  of  entering  air  can 

be  utilized  for  warming  purposes.  Therefore,  if  we  divide  the  com- 
puted heat  loss  in  B.  T.  U.  from  a  room,  by  .9,  it  will  give  the  number 
of  cubic  feet  of  air  at  120  degrees  necessary  to  warm  the  room  in  zero 
weather. 

As  the  outside  temperature  becomes  colder,  the  quantity  of  heat 
brought  in  per  cubic  foot  of  air  increases;  but  the  proportion  avail- 
able for  warming  purposes  becomes  less  at  nearly  the  same  rate,  so 

TABLE  VIII 
Warm=Air  Pipe  Dimensions 


DIAMETER  OF  PIPE, 
IN  INCHES 

AREA                     AREA 
IN  SQUARE  INCHES           IN  SQUARE  FEET 

6 

28                  .196 

7 

38 

.267 

8 

50 

.349 

9                   64 

.442 

10 

79 

.545 

11 

95 

.660 

12 

113 

.785 

13 

133 

.922 

14 

154 

1.07 

15 

177 

1.23 

16 

201 

1.40 

HEATING  AND  VENTILATION  31 

that  for  all  practical  purposes  we  may  use  the  figure  .9  for  all  usual 
conditions.  In  calculating  the  size  of  pipe  required,  we  may  assume 
maximum  velocities  of  260  and  380  feet  per  minute  for  rooms  on  the 
first  and  second  floors  respectively.  Knowing  the  number  of  cubic 
feet  of  air  per  minute  to  be  delivered,  we  can  divide  it  by  the  velocity, 
which  will  give  us  the  required  area  of  the  pipe  in  square  feet. 

Round  pipes  of  tin  or  galvanized  iron  are  used  for  this  purpose. 
Table  VIII  will  be  found  useful  in  determining  the  required  diameters 
of  pipe  in  inches. 

Example.  The  heat  loss  from  a  room  on  the  second  floor  is  18,000  B. 
T.  U.  per  hour.  What  diameter  of  warm -air  pipe  will  be  required? 

18,000  -^  .9  =  20,000  =  cubic  feet  of  air  required  per  hour. 
20,000  -^  60  =  333  per  minute.  Assuming  a  velocity  of  380  feet 
per  minute,  we  have  333  -=-  380  =  .87  square  foot,  which  is  the 
area  of  pipe  required.  Referring  to  Table  VIII,  we  find  this  comes 
between  a  12-inch  and  a  13-inch  pipe,  and  the  larger  size  would 
probably  be  chosen. 

EXAMPLES  FOR   PRACTICE 

1.  A  first-floor  room  has  a  computed  loss  of  27,000  B.  T.  U. 
per  hour  when  it  is  10°  below  zero.     The  air  for  warming  is  to  enter 
through  two  pipes  of  equal  size,  and  at  a  temperature  of  120  degrees. 
What  will  be  the  required  diameter  of  the  pipes? 

ANS.     14  inches. 

2.  If  in  the  above  example  the  room  had  been  on  the  second 
floor,  and  the  air  was  to  be  delivered  through  a  single  pipe,  what 
diameter  would  be  required? 

ANS.     16  inches. 

Since  long  horizontal  runs  of  pipe  increase  the  resistance  and 
loss  of  heat,  they  should  not  in  general  be  over  12  or  14  feet  in  length. 
This  applies  especially  to  pipes  leading  to  rooms  on  the  first  floor, 
or  to  those  on  the  cold  side  of  the  house.  Pipes  of  excessive  length 
should  be  increased  in  size  because  of  the  added  resistance. 

Figs.  10  and  11  show  common  methods  of  running  the  pipes  in 
the  basement.  The  first  gives  the  best  results,  and  should  be  used 
where  the  basement  is  of  sufficient  height  to  allow  it.  A  damper 
should  be  placed  in  each  pipe  near  the  furnace,  for  regulating  the  flow 
of  air  to  the  different  rooms,  or  for  shutting  it  off  entirely  when  desired. 


327 


HEATING  AND  VENTILATION 


While  round  pipe  risers  give  the  best  results,  it  is  not  always 
possible  to  provide  a  sufficient  space  for  them,  and  flat  or  oval  pipes 
are  substituted.  When  vertical  pipes  must  be  placed  in  single  par- 
titions, much  better  results  will  be  obtained  if  the  studding  can  be 


Fig.  10.  Fig.  11. 

Common  Methods  of  Running  Hot-Air  Pipes  in  Basement.    Method  Shown  in  Fig.  10 
is  Preferable  where  Feasible. 

made  5  or  6  inches  deep  instead  of  4  as  is  usually  done.  Flues  should 
never  in  any  case  be  made  less  than  3i  inches  in  depth.  Each  room 
should  be  heated  by  a  separate  pipe.  In  some  cases,  however,  it  is 
allowable  to  run  a  single  riser  to  heat  two  unimportant  rooms  on  an 
upper  floor.  A  clear  space  of  at  least  •>-  inch  should  be  left  between 
the  risers  and  studs,  and  the  latter  should  be  carefully  tinned,  and  the 

TABLE  IX 
Dimensions  of  Oval  Pipes 


DIMENSION-  OF  PIP 

E                                            AREA  IN  SQUARE  INCHES 

6  ovalocl  to  5    i 

27 

7       "       "4 

31 

7       "       "  31 

29 

7        "       "  6" 

38 

S        "         '   5 

43 

0                  '4 

4.5 

9      "      •  r> 

57 

0        "         '   o 

51 

10        "         '  3.V 

46 

11        "         '4 

58 

12       "         '  3* 

55 

10        "        "  6 

67 

11        "'        "  5 

67 

14        '•        "  4 

76 

1           "        "  3V 

73 

1          "       "  6" 

So 

1              "          "    ;'j 

75 

,,            ..          ..    4 

96 

2,      ••     "  :u 

100 

228 


HEATING  AN.D  VENTILATION 


33 


space  between  them  on  both  sides  covered  with  tin,  asbestos,  or  wire 
lath. 

Table  IX  gives  the  capacity  of  oval  pipes.  A  6-inch  pipe  ovaled 
to  5  means  that  a  6-inch  pipe  has  been  flattened  out  to  a  thickness  of 
5  inches,  and  column  2  gives  the  resulting  area. 

Having  determined  the  size  of  round  pipe  required,  an  equiva- 
lent oval  pipe  can  be  selected  from  the  table  to  suit  the  space  available. 

Registers.  The  registers  which  control  the  supply  of  warm 
air  to  the  rooms,  generally  have  a  net  area  equal  to  two-thirds  of  their 
gross  area.  The  net  area  should  be  from  10  to  20  per  cent  greater 
than  the  area  of  the  pipe  connected  with  it.  It  is  common  practice 
to  use  registers  having  the  short  dimensions  equal  to,  and  the  long 
dimensions  about  one-half  greater  than,  the  diameter  of  the  pipe. 
This  would  give  standard  sizes  for  different  diameters  of  pipe,  as 
listed  in  Table  X. 

TABLE  X 
Sizes  of  Registers  for  Different  Sizes  of  Pipes 


DIAMETER  OF  PIPE 


SIZE  OF  REGISTER 


6  i 

n. 

6  X  10  i 

n. 

7 

' 

7  X  10  ' 

8 

' 

8  X  12 

9 

< 

9  X  14 

10 

' 

10  X  15 

11 

' 

11  X  16 

12 

1 

12  X  17 

13 

' 

14  X  20 

14 

' 

14  X  22 

15 

1 

15  X  22 

16 

16  X  24 

Combination  Systems.  A  combination  system  for  heating  by 
hot  air  and  hot  water  consists  of  an  ordinary  furnace  with  some  form 
of  surface  for  heating  water,  placed  either  in  contact  with  the  fire  or 
suspended  above  it.  Fig.  12  shows  a  common  arrangement  where 
part  of  the  heating  surface  forms  a  portion  of  the  lining  to  the  firepot 
and  the  remainder  is  above  the  fire. 

Care  must  be  taken  to  proportion  properly  the  work  to  be  done 
by  the  air  and  the  water;  else  one  will  operate  at  the  expense  of  the 
other.  One  square  foot  of  heating  surface  in  contact  with  the  fire  is 
capable  of  supplying  from  40  to  50  square  feet  of  radiating  surface, 


129 


HEATING  AND  VENTILATION 


and  one  square  foot  suspended  over  the  fire  will  supply  from  15  to  25 
square  feet  of  radiation. 

The  value  or  efficiency  of  the  heating  surface  varies  so  widely  in 
different  makes  that  it  is  best  to  state  the  required  conditions  to  the 


Fig.  12.    Combination  Furnace,  for  Heating  by  Both  Hot  Air  and  Hot  Water. 

manufacturers  and  have  them  proportion  the  surfaces  as  their  experi- 
ence has  found  best  for  their  particular  type  of  furnace. 

Care  and  Management  of  Furnaces.  The  following  general 
rules  apply  to  the  management  of  all  hard  coal  furnaces. 

The  fire  should  be  thoroughly  shaken  once  or  twice  daily  in  cold 
weather.  It  is  well  to  keep  the  firepot  heaping  full  at  all  tiroes.  In 


230 


HEATING  AND  VENTILATION  35 


this  way  a  more  even  temperature  may  be  maintained,  less  attention  is 
required,  and  no  more  coal  is  burned  than  when  the  pot  is  only  partly 
filled.  In  mild  weather  the  mistake  is  frequently  made  of  carrying  a 
thin  fire,  which  requires  frequent  attention  and  is  likely  to  die  out. 
Instead,  to  diminish  the  temperature  in  the  house,  keep  the  firepot 
full  and  allow  ashes  to  accumulate  on  the  grate  (not  under  it)  by  shak- 
ing less  frequently  or  less  vigorously.  The  ashes  will  hold  the  heat 
and  render  it  an  easy  matter  to  maintain  and  control  the  fire.  When 
feeding  coal  on  a  low  fire,  open  the  drafts  and  neither  rake  nor  shake 
the  fire  till  the  fresh  coal  becomes  ignited.  The  air  supply  to  the  fire 
is  of  the  greatest  importance.  An  insufficient  amount  results  in  incom- 
plete combustion  and  a  great  loss  of  heat.  To  secure  proper  combus- 
tion, the  fire  should  be  controlled  principally  by  means  of  the  ash-pit 
through  the  ash-pit  door  or  slide. 

The  smoke-pipe  damper  should  be  opened  only  enough  to  carry 
off  the  gas  or  smoke  and  to  give  the  necessary  draft.  The  openings 
in  the  feed  door  act  as  a  check  on  the  fire,  and  should  be  kept  closed 
during  cold  weather,  except  just  after  firing,  when  with  a  good  draft 
they  may  be  partly  opened  to  increase  the  air-supply  and  promote  the 
proper  combustion  of  the  gases. 

Keep  the  ash-pit  clear  to  avoid  warping  or  melting  the  grate. 
The  cold-air  box  should  be  kept  wide  open  except  during  winds  or 
when  the  fire  is  low.  At  such  times  it  may  be  partly,  but  never  com- 
pletely closed.  Too  much  stress  cannot  be  laid  on  the  importance 
of  a  sufficient  air-supply  to  the  furnace.  It  costs  little  if  any  more 
to  maintain  a  comfortable  temperature  in  the  house  night  and  day 
than  to  allow  the  rooms  to  become  so  cold  during  the  night  that  the 
fire  must  be  forced  in  the  morning  to  warm  them  up  to  a  comfortable 
temperature. 

In  case  the  warm  air  fails  at  times  to  reach  certain  rooms,  it 
may  be  forced  into  them  by  temporarily  closing  the  registers  in  other 
rooms.  The  current  once  established  will  generally  continue  after 
the  other  registers  have  been  opened. 

It  is  best  to  burn  as  hard  coal  as  the  draft  will  warrant.  Egg 
size  is  better  than  larger  coal,  since  for  a  given  weight  small  lumps 
expose  more  surface  and  ignite  more  quickly  than  larger  ones.  The 
furnace  and  smoke-pipe  should  be  thoroughly  cleaned  once  a  year. 


36  HEATING  AND  VENTILATION 


This  should  he  done  just  after  the  fire  has  been  allowed  to  go  out  in 
the  spring. 

STEAM    BOILERS 

Types.  The  boilers  used  for  heating  are  the  same  as  have  already 
been  described  for  power  work.  In  addition  there  is  the  oast-iron 
sectional  boiler,  used  almost  exclusively  for  dwelling-houses. 

Tubular  Boilers.  Tubular  boilers  are  largely  used  for  heating 
purposes,  and  are  adapted  to  all  classes  of  buildings  except  dwelling- 
houses  and  the  special  cases  mentioned  later,  for  which  sectional 
boilers  are  preferable.  A  boiler  horse-pou-cr  has  been  defined  as  the 
evaporation  of  34?  pounds  of  water  from  and  at  a  temperature  of  212 
degrees,  and  in  doing  this  33,317  B.  T.  U.  are  absorbed,  which  are 
again  given  out  when  the  steam  is  condensed  in  the  radiators.  Hence 
to  find  the  boiler  H.  P.  required  for  warming  any  given  building,  we 
have  only  to  compute  the  heat  loss  per  hour  by  the  methods  already 
given,  and  divide  the  result  by  33,330.  It  is  more  common  to  divide 
by  the  number  33,000,  which  gives  a  slightly  larger  boiler  and  is  on 
the  side  of  safety. 

The  commercial  horse-power  of  a  well-designed  boiler  is  based 
upon  its  heating  surface;  and  for  the  best  economy  in  heating  work, 
it  should  be  so  proportioned  as  to  have  about  1  square  foot  heating  of 
surface  for  each  2  pounds  of  water  to  be  evaporated  from  and  at  212 
degrees  F.  This  gives  34.5  -=-  2  =  17.2  square  feet  of  heating  surface 
per  horse-power,  which  is  geNerally  taken  as  1  5  in  practice.  Makers  of 
tubular  boilers  commonly  rate  them  on  a  basis  of  12  square  feet  of  heat- 
ing surface  per  horse-power.  This  is  a  safe  figure  under  the  conditions 
of  power  work,  where  skilled  firemen  are  employed  and  where  more 
care  is  taken  to  keep  the  heating  surfaces  free  from  soot  and  ashes. 
For  heating  plants,  however,  it  is  better  to  rate  the  boilers  upon  15 
square  feet  per  horse-power  as  stated  above. 

There  is  some  difference  of  opinion  as  to  the  proper  method  of 
computing  the  heating  surface  of  tubular  boilers.  In  general,  all 
surface  is  taken  which  is  exposed  to  the  hot  gases  on  one  side  and  to 
the  water  on  the  other.  A  safe  rule,  and  the  one  by  which  Table 
XII  is  computed,  is  to  take  J  the  area  of  the  shell,  f  of  the  rear  head, 
less  the  tube  area,  and  the  interior  surface  of  all  the  tubes. 

The  required  amount  of  grate  area,  and  the  proper  ratio  of  heat- 


232 


HEATING  AND  VENTILATION 


ing  surface  to  grate  area,  vary  a  good  deal,  depending  on  the  character 
of  the  fuel  and  on  the  chimney  draft.  By  assuming  the  probable 
rates  of  combustion  and  evaporation,  we  may  compute  the  required 
grate  area  for  any  boiler  from  the  formula : 

H.P.  x  34.5 

E  XC         > 
in  which 

S  =  Total  grate  area,  in  square  feet; 

E  =  Pounds  of  water  evaporated  per  pound  of  coal ; 

C  =  Pounds  of  coal  burned  per  square  foot  of  grate  per  hour. 

Table  XI  gives  the  approximate  grate  area  per  H.  P.  for  different 
rates  of  evaporation  and  combustion  as  computed  by  the  above 
equation. 

TABLE  XI 

Grate   Area  per   Horse-Power  for  Different  Rates  of  Evaporation  and 
Combustion 

i 

POUNDS  OF  COAL  BURNED  PER  SQUARE  FOOT  OF  GRATE  PER  HOUR 


POUNDS  OP  STEAM  PER 
POUND  OF  COAL 

8  Ibs. 

10  Ibs.                            12  Ibs. 

Square  Feet  of  Grate  Surface  per  Horse-  Power 

10 

.43 

.35 

.28 

9 

.48 

.38 

.  32 

8 

.54 

.43 

.36 

7 

.62 

.49 

.41 

6 

.72 

.58 

.48 

For  example,  with  an  evaporation  of  8  pounds  of  steam  per  pound  of 
coal,  and  a  combustion  of  10  pounds  of  coal  per  square  foot  of  grate,  .43  of  a 
square  foot  of  grate  surface  per  H.  P.  would  be  called  for. 

The  ratio  of  heating  to  grate  surface  in  this  type  of  boiler  ranges 
from  30  to  40,  and  therefore  allows  under  ordinary  conditions  a  com- 
bustion of  from  8  to  10  pounds  of  coal  per  square  foot  of  grate.  This 
is  easily  obtained  with  a  good  chimney  draft  and  careful  firing.  The 
larger  the  boiler,  the  more  important  the  plant  usually,  and  the  greater 
the  care  bestowed  upon  it,  so  that  we  may  generally  count  on  a  higher 
rate  of  combustion  and  a  greater  efficiency  as  the  size  of  the  boiler 
increases.  Table  XII  will  be  found  very  useful  in  determining 
the  size  of  boiler  required  under  different  conditions.  The  grate 
area  is  computed  for  an  evaporation  of  8  pounds  of  water  per  pound 


233 


38 


HEATING  AND  VENTILATION 


TABLE   XII 


DlWKTFK 

SIZE  OF 

SIZE  OF 

OF  SHELL 
IN    INCHES 

OF  TUBES     QFTi-HKs 
IN    INCHES 

OF  TUBES 
IN    FEET 

POWER 

GRATE  IN 
,     INCHES 

UPTAKE 
IN  INCHES 

SMOKE- 
PIPE  IN 
SQ.  IN 

30 

28             -2y2 

6 

8.5 

24  x  36 

10x14 

140 

7 

9.9 

.  24  x  36 

10x14 

140 

8 

11.2 

24  x  36 

10x14 

140 

9 

12.6 

24  x  42 

10x14 

140 

10 

14.0 

24  x  42 

10x14 

140 

86 

34         iy, 

8 

13.6 

i  30  x  36 

10x16 

160 

9 

15.3 

30  x  42 

10x18 

180 

10 

16.9 

30  x  42 

10x18 

180 

11 

18.6 

30  x  48 

10  x  20 

200 

12 

20.9 

30  x  48 

10  x  20 

200 

42 

:>4                3 

9 

18.5 

86  x  42 

10x20 

200 

10 

20.5 

86  x  42 

10  x  20 

200 

11 

22.5 

36  x  48 

10  x  25 

250 

12 

24.5 

36  x  48 

10  x  25 

250 

13 

26.5 

36  x  48 

10x28 

280 

14 

'     28.5 

36  x  54 

10x28 

280 

48 

44                3 

10 

30.4 

42x48 

10x28 

280 

11 

33  2 

42  x  48 

10  x  28 

280 

12 

85.7 

42  x  54 

10  x  32 

320 

13 

38.3 

42  x  54 

10x32 

320 

14 

40.8 

42x60 

10x36 

360 

15 

43.4 

42  x  60 

10  x  36 

360 

16 

45.9 

42  x  60 

10x36 

360 

54 

54                3 

11 

34.6 

48  x  54 

10  x  38 

3SO 

12 

87  .  7 

48  x  54 

10  x  38 

380 

13 

40.8 

48  x  54 

10  x  38 

380 

14 

43.9 

48  x  54 

10x38 

380 

15 

47.0 

48  x  60 

10  x  40 

400 

16 

50.1 

48x60 

10x40 

400 

46              \\y. 

'   17 

53.0 

48x60 

10x40 

400 

60 

72                8 

12 

48.4 

54  x  60 

12x40 

460 

13 

52.4 

54  x  60 

12x40 

460 

14 

56.4 

54  x60 

12x40 

460 

15 

60.4 

54  x  66 

12x42 

500 

16 

64.4 

54  x  66 

12  x  42 

500 

64              31^ 

17 

71.4 

54  x  72 

12x48 

550 

18 

75  .  6 

54  x  72 

12x48 

550 

66 

90                3 

14 

70.1 

60x66 

12x48 

500 

15 

75.0 

60  x  72 

12x52 

620 

16 

80.0 

60  x  72 

12x52 

620 

78             3y2 

17 

86.0 

60x78 

12  x  56 

670 

18 

91.1 

60x78 

12x56 

670 

19 

96.2 

60  x  78 

12x56 

670 

62               4 

20 

93.1 

60x78 

12x56 

670 

72 

'  114               3 

14 

87.4 

66  x  72 

12  x  56 

670 

15 

93.6 

66  x  72 

12x56 

670 

16 

99.7 

66  x78 

12  x62 

740 

98             3i^ 

17 

106.4 

66  x  78 

12x62 

740 

18 

112.6 

66  x  84 

12x66 

790 

19 

118.8 

66  x  84 

12  x  66 

790 

72               4 

20 

107.3 

66x84 

12x66 

790 

234 


DIRECT-INDIRECT    SYSTEM    OF    WARMING,    SHOWING    ADJUSTABLE    DAMPER. 
American  Radiator  Company. 


MEATING  AND  VENTILATION  39 

of  coal,  which  corresponds  to  an  efficiency  of  about  60  per  cent,  and 
is  about  the  average  obtained  in  practice  for  heating  boilers. 

The  areas  of  uptake  and  smoke-pipe  are  figured  on  a  basis  of 
1  square  foot  to  7  square  feet  of  grate  surface,  and  the  results  given 
in  round  numbers.  In  the  smaller  sizes  the  xelative  size  of  smoke- 
pipe  is  greater.  The  rate  of  combustion  runs  from  6  pounds  in  the 
smaller  sizes  to  11£  in  the  larger.  Boilers  of  the  proportions  given 
in  the  table,  correspond  well  with  those  used  in  actual  practice,  and 
may  be  relied  upon  to  give  good  results  under  all  ordinary  conditions. 

Water-tube  boilers  are  often  used  for  heating  purposes,  but  more 
especially  in  connection  with  power  plants.  The  method  of  com- 
puting the  required  H.  P.  is  the  same  as  for  tubular  boilers. 

Sectional  Boilers.  Fig.  13  shows  a  common  form  of  cast-iron 
boiler.  It  is  made  up  of  slabs  or  sections,  each  one  of  which  is  con- 
nected by  nipples  with  headers  at  the  sides  and  top.  The  top  header 
acts  as  a  steam  drum,  and  the  lower  ones  act  as  mud  drums;  they  also 
receive  the  water  of  condensation  from  the  radiators.  The  gases 
from  the  fire  pass  backward  and  forward  through  flues  and  are  finally 
taken  off  at  the  rear  of  the  boiler. 

Another  common  form  of  sectional  boiler  is  shown  in  Fig.  14. 
It  is  made  up  of  sections  which  increase  the  length  like  the  one  just 
described.  These  boilers  have  no  drum  connecting  with  the  sections; 
but  instead,  each  section  connects  with  the  adjacent  one  through 
openings  at  the  top  and  bottom,  as  shown. 

The  ratio  of  heating  to  grate  surface  in  boilers  of  this  type  ranges 
from  15  to  25  in  the  best  makes.  They  are  provided  with  the  usual 
attachments,  such  as  pressure-gauge,  water-glass,  gauge-cocks,  and 
safety-valve;  a  low-pressure  damper  regulator  is  furnished  for  operat- 
ing the  draft  doors,  thus  keeping  the  steam  pressure  practically  con- 
stant. A  pressure  of  from  1  to  5  pounds  is  usually  carried  on  these 
boilers,  depending  upon  the  outside  temperature.  The  usual  setting 
is  simply  a  covering  of  some  kind  of  non-conducting  material  like 
plastic  magnesia  or  asbestos,  although  some  forms  are  enclosed  in 
light  brickwork. 

In  computing  the  required  size,  we  may  proceed  in  the  same 
manner  as  in  the  case  of  a  furnace.  For  the  best  types  of  house- 
heating  boilers,  we  may  assume  &  combustion  of  5  pounds  of  coal  per 
square  foot  of  grate  per  hour,  and  an  average  efficiency  of  GO  per  cent, 


235 


HEATING  AND  VENTILATION 


which  corresponds  to  S,000  B.  T.  U.  per  pound  of  coal,  available  for 
useful  work. 

In  the  case  of  direct-steam  heating,  we  have  only  to  supply  heat 
to  offset  that  lost  by  radiation  and  conduction ;  so  that  the  grate  area 
may  be  found  by  dividing  the  computed  heat  loss  per  hour  by  8,000, 
which  gives  the  number  of  pounds  of  coal;  and  this  in  turn,  divided 
by  5,  will  give  the  area  of  grate  required.  The  most  efficient  rate  of 


Fig.  13.    Commo 


Headers  at  Sides  and  Top 


combustion  will  depend  somewhat  upon  the  ratio  between  the  grate 
and  heating  surface.  It  has  been  found  by  experience  that  about  4 
of  a  pound  of  coal  per  hour  for  each  square  foot  of  heating  surface 
gives  the  best  results;  so  that,  by  knowing  the  ratio  of  heating  surface 
to  grate  area  for  any  make  of  heater,  we  can  easily  compute  the  most 
efficient  rate  of  combustion,  and  from  it  determine  the  necessar  rate 


HEATING  AND  VENTILATION 


11 


For  example,  suppose  the  heat  loss  from  a  building  to  be  480,000 
B.  T.  U.  per  hour,  and  that  we  wish  to  use  a  heater  in  which  the  ratio 
of  heating  surface  to  grate  area  is  24.  What  will  be  the  most  efficient 
rate  of  combustion  and  the  required 
grate  area?  480,000  -5-  8,000  -  60 
pounds  of  coal  per  hour,  and  24  -T-  4 
=  6,  which  is  the  best  rate  of  com- 
bustion to  employ;  therefore  60  -f-  6 
=  10,  the  grate  area  required. 

There  are  many  different  designs 
of  cast-iron  boilers  for  low-pressure 
steam  and  hot-water  heating.  In  gen- 
eral, boilers  having  a  drum  connected 
by  nipples  with  each  section  give 
dryer  steam  and  hold  a  steadier  water- 
line  than  the  second  form,  especially 
when  forced  above  their  normal  ca- 
pacity. The  steam,  in  passing  through 
the  openings  between  successive  sec- 
tions in  order  to  reach  the  outlet, 

is  apt  to  carry  with  it  more  or  less  water,  and  to  choke  the  openings, 
thus  producing  an  uneven  pressure  in  different  parts  of  the  boiler. 

In  the  case  of  hot-water  boilers  this  objection  disappears. 

In  order  to  adapt  this  type  of  boiler  to  steam  work,  the  opening 
between  the  sections  should  be  of  good  size,  with  an  ample  steam 
space  above  the  water-line;  and  the  nozzles  for  the  discharge  of  steam 
should  be  located  at  frequent  intervals. 


Fig.  14.    Another.  Type  of  Sectional 
Boiler.  Here  there  are  no  drums, 
the  sections   being   directly 
connected  through  open- 
ings at  top  and  bottom. 
Courtesy  of  American  Radiator  Co. 


EXAMPLES    FOR    PRACTICE 

1.  The  heat  loss  from  a  building  is  240,000  B.  T.  U.  per  hour, 
and  the  ratio  of  heating  to  grate  area  in  the  heater  to  be  used  is  20. 
What  will  be  the  required  grate  area?  ANS.  6  sq.  ft. 

2.  The  heat  loss  from  a  building  is  168,000  B.  T.  U.  per  hour,  and 
the  chimney  draft  is  such  that  not  over  3  pounds  of  coal  per  hour  can 
be  burned  per  square  foot  of  grate.     What  ratio  of  heating  to  grate 
area  will  be  necessary,  and  what  will  be  the  required  grate  area? 

ANS.  Ratio,  12.     Grate  area,  7  sq.  ft. 


42  HEATING  AND  VENTILATION 

Cast-iron  sectional  boilers  are  used  for  dwelling-houses,  small 
schoolhouses,  churches,  etc.,  where  low  pressures  are  carried.  They 
are  increased  in  size  by  adding  more  slabs  or  sections.  After  a  certain 
length  is  reached,  the  rear  sections  become  less  and  less  efficient,  thus 
limiting  the  size  and  power. 

Horse=Po\ver  for  Ventilation.  We  already  know  that  one 
B.  T.  U.  will  raise  the  temperature  of  1  cubic  foot  of  air  55  degrees, 
or  it  will  raise  100  cubic  feet  T-J-T  of  55  degrees,  or  ^/V  of  1  degree; 
therefore,  to  raise  100  cubic  feet  1  degree,  it  will  take  1  -r-  -**$,  or  y1/ 
B.  T.  U.;  and  to  raise  100  cubic  feet  through  100  degrees,  it  will  take 
yy  x  100  B.  T.  U.  In  other  words,  the  B.  T.  U.  required  to  raise 
any  given  volume  of  air  through  any  number  of  degrees  in  tempera- 
ture, is  equal  to 

Volume  of  air  in  cubic  ft.   X  Degrees  raised 
55 

Example.  How  many  B.  T.  V.  are  required  to  raise  100,000 
cubic  feet  of  air  70  degrees? 

100,000  X  70  _127272_{ 
55 

To  compute  the  H.  P.  required  for  the  ventilation  of  a  building, 
we  multiply  the  total  air-supply,  in  cubic  feet  per  hour,  by  the  number 
of  degrees  through  which  it  is  to  be  raised,  and  divide  the  result  by  55. 
This  gives  the  B.  T.  U.  per  hour,  which,  divided  by  33,000,  will  give 
the  II.  P.  required.  In  using  this  rule,  always  take  the  air-supply  in 
cubic  feet  per  hour. 

EXAMPLES  FOR  PRACTICE 

1.  The  heat  loss  from  a  building  is  1,050,000  B.  T.  U.  per  hour. 
There  is  to  be  an  air-supply  of  1,500,000  cubic  feet  per  hour,  raised 
through  70  degrees.     What  is  the  total  boiler  H.  P.  required? 

Axs.  10S. 

2.  A  high  school  has  10  classrooms,  each  occupied  by  50  pupils. 
Air  is  to  be  delivered  to  the  rooms  at  a  temperature  of  70  degrees. 
What  will  be  the  total  H.  P.  required  to  heat  and  ventilate  the  building 
when  it  is  10  degrees  below  zero,  if  the  heat  loss  through  walls  and 
windows  is  1,320,000  B.  T.  U.  per  hour?  Axs.   100-f-. 

DIRECT=STEAM  HEATING 

A  system  of  direct-steam  heating  consists  (1)  of  a  furnace  and 


HEATING  AND  VENTILATION 


boiler  for  the  combustion  of  fuel  and  the  generation  of  steam;  (2)  a 
system  of  pipes  for  conveying  the  steam  to  the  radiators  and  for 
returning  the  water  of  condensation  to  the  boiler;  and  (3)  radiators 
or  coils  placed  in  the  rooms  for  diffusing  the  heat. 

Various  types  of  boilers  are  used,  depending  upon  the  size  and 
kind  of  building  to  be  warmed.  Some  form  of  cast-iron  sectional 
boiler  is  commonly  used  for  dwelling-houses,  while  the  tubular  or 
water-tube  boiler  is  more  usually  employed  in  larger  buildings. 
Where  the  boiler  is  used  for  heating  purposes  only,  a  low  steam-pres- 
sure of  from  2  to  10  pounds  is  carried,  and  the  condensation  flows 
back  by  gravity  to  the  boiler,  which  is  placed  below  the  lowest  radiator. 
When,  for  any  reason,  a  higher 
pressure  is  required,  the  steam  for 
the  heating  system  is  made  to 
pass  through  a  reducing  valve, 
and  the  condensation  is  returned 
to  the  boiler  by  means  of  a  pump 
or  return  trap. 

Types  of  Radiating  Surface. 
The  radiation  used  indirect-steam 
heating  is  made  up  of  cast-iron 
radiators  of  various  forms,  pipe 
radiators,  and  circulation  coils. 

Cast=Iron  Radiators.  The 
general  form  of  a  cast-iron  sec- 
tional radiator  is  shown  in  Fig. 
15.  Radiators  of  this  type  are 
made  up  of  sections,  the  number 

depending  upon  the  amount  of  heating  surface  required.  Fig.  16 
shows  an  intermediate  section  of  a  radiator  of  this  type. 
It  is  simply  a  loop  with  inlet  and  outlet  at  the  bottom^  The 
end  sections  are  the  same,  except  that  they  have  legs,  as  shown  in 
Fig.  17.  These  sections  are  connected  at  the  bottom  by  special 
nipples,  so  that  steam  entering  at  the  end.  fills  the  bottom  of  the 
radiator,  and,  being  lighter  than  the  air,  rises  through  the  loops  and 
forces  the  air  downward  and  toward  the  farther  end,  where  it  is  dis-* 
charged  through  an  air-valve  placed  about  midway  of  the  last  section. 
There  are  many  different  designs  varying  in  height  and  width,  te 


Fig.  15.     Common  Type  of  Cast-Iron 
Sectional  Radiator. 


839 


44 


HEATING  AND  VENTILATION 


suit  all  conditions.     The  wall  pattern  shown  in  Fig.  18  is  very  con- 
venient when  it  is  desired  to  place  the  radiator  above  the  floor,  as  in 

bathrooms,  etc.;  it  is  also  a  con- 
venient form  to  place  under  the 
window's  of  halls  and  churches 
to  counteract  the  effect  of  cold 
down  drafts.  It  is  adapted  to 
nearly  every  place  where  the  or- 
dinary direct  radiator  can  be 
used,  and  may  be  connected  up 
in  different  ways  to  meet  the  va- 
rious requirements. 

A  low  and  moderately  shallow 
radiator,  with  ample  space  for  the 
circulation  of  air  between  the 
sections,  is  more  efficient  than  a 
deep  radiator  writh  the  sections 
closely  packed  together.  One- 
and  two-column  radiators,  so 
called,  are  preferable  to  three- 
sufficient  space  to  use  them. 


o 


^ 


Fig.  16. 


rig.  IT 


Intermediate  and  End  Sections  of  Kadi; 
Shown  in  Fig.  15.     The  end  sections 
(at  right)  have  legs. 


and  four-column,  when  there 

f 


Fig.  18.    Cast-iron  Sectional  Radiator  of  Wall  Pattern. 

The  standard  height  of  a  radiator  is  36  or  38  inches,  and,  if 
possible,  it  is  better  not  to  exceed  this. 


240 


HEATING  AND  VENTILATION 


For  small  radiators,  it  is  better  practice  to  use  lower  sections  and 
increase  the  length;  this  makes  the  radiator  slightly  more  efficient 
and  gives  a  much  better  appearance. 

To  get  the  best  results  from  wall  radiators,  they  should  be  set 
out  at  least  H  inches  from  the  wall  to  allow  a  free  circulation  of  air 
back  of  them.  Patterns  having  cross-bars  should  be  placed,  if 
possible,  with  the  bars  in  a  vertical  position,  as  their  efficiency  is 
impaired  somewhat  when  placed  horizontally. 

Pipe  Radiators.  This  type  of  radiator  (see  Fig.  19)  is  made  up  of 
wrought-iron  pipes 
screwed  into  a  cast- 
iron  base.  The 
pipes  are  either  con- 
nected in  pairs  at 
the  top  by  return 
bends,  or  each  sep- 
arate tube  has  a 
thin  metal  dia- 
phragm passing  up 
the  center  nearly  to 
the  top.  It  is  nec- 
essary that  a  loop 
be  formed,  else  a 
"dead  end"  would 
occur.  This  would 
become  filled  with 
air  a  n  d  prevent 
steam  from  enter- 
ing, thus  causing  portions  of  the  radiator  to  remain  cold. 

Circulation  Coils.  These  are  usually  made  up  of  1  or  lj-inch 
wrought-iron  pipe,  and  may  be  hung  on  the  walls  of  a  room  by  means 
of  hook  plates,  or  suspended  overhead  on  hangers  and  rolls. 

Fig.  20  shows  a  common  form  for  schoolhouse  and  similar  work; 
this  coil  is  usually  made  of  lj-inch  pipe  screwed  into  headers  or 
branch  tees  at  the  ends,  and  is  hung  on  the  wall  just  below  the  windows. 
This  is  known  as  a  branch  coil.  Fig.  21  shows  a  trombone  coil,  which 
is  commonly  used  when  the  pipes  cannot  turn  a  corner,  and  where 
the  entire  coil  must  be  placed  upon  one  side  of  the  room.  Fig.  22 


Fig.  1£K    Wrought-iron  Pipe  Radiator. 


341 


HEATING  AND  VENTILATION 


is  called  a  miter  coil,  and  is  used  under  the  same  conditions  as  a  trom- 
bone coil  if  there  is  room  for  the  vertical  portion.  This  form  is  not 
so  pleasing  in  appearance  as  either  of  the  other  two,  and  is  found  only 
in  factories  or  shops,  where  looks  are  of  minor  importance. 


Fig.  20.    Common  Form  of  '•  Branch' '  Coil  for  Circulation  of  Direct  Steam. 

Overhead  coils  are  usuallv  of  the  miter  form,  laid  on  the  side  and 
suspended  about  a  foot  from  the  ceiling;  they  are  less  efficient  than 
when  placed  nearer  the  floor,  as  the  warm  air  stays  at  the  ceiling  and 
the  lower  part  of  the  room  is  likely  to  remain  cold.  They  are  used 


Fig.  21.     "Trombone'' Coil.     Used  where  Entire  Coil  must  be  Placed  on  One  Side  <  f  Room 

only  when  wall  coils  or  radiators  would  be  in  the  way  of  fixtures,  or 
when  they  would  come  below  the  water-line  of  the  boiler  if  placed 
near  the  floor. 

When  steam  is  first  turned  on  a  coil,  it  usually  passes  through  a 


Fig.  22.    "Miter"  Coil.    Adapted,  like  the  "Trombone."  Only  to  a  Single  Wall. 
Frequently  Used  in  Factories  and  Shops. 

portion  of  the  pipes  first  and  heats  them  while  the  others  remain  cold 
and  full  of  air.  Therefore  the  coil  must  always  be  made  up  in  such 
a  way  that  each  pipe  shall  have  a  certain  amount  of  spring  and  may 
expand  independently  without  bringing  undue  strains  upon  the  others. 
Circulation  coils  should  incline  about  1  inch  in  20  feet  toward  the 


242 


HEATING  AND  VENTILATION  47 

return  end  in  order  to  secure  proper  drainage  and  quietness  of  opera- 
tion. 

Efficiency  of  Radiators.  The  efficiency  of  a  radiator — that  is, 
the  B.  T.  U.  which  it  gives  off  per  square  foot  of  surface  per  hour — 
depends  upon  the  difference  in  temperature  between  the  steam  in  the 
radiator  and  the  surrounding  air,  the  velocity  of  the  air  over  the 
radiator,  and  the  quality  of  the  surface,  whether  smooth  or  rough. 
In  ordinary  low-pressure  heating,  the  first  condition  is  practically 
constant;  but  the  second  varies  somewhat  with  the  pattern  of  the 
radiator.  An  open  design  which  allows  the  air  to  circulate  freely 
over  the  radiating  surfaces,  is  more  efficient  than  a  closed  pattern, 
and  for  this  reason  a  pipe  coil  is  more  efficient  than  a  radiator. 

In  a  large  number  of  tests  of  cast-iron  and  pipe  radiators,  working 
under  usual  conditions,  the  heat  given  off  per  square  foot  of  surface 
per  hour  for  each  degree  difference  in  temperature  between  the  steam 
and  surrounding  air  was  found  to  average  about  1 . 7  B.  T.  U.  The 
temperature  of  steam  at  3  pounds'  pressure  is  220  degrees,  and  220 — 70 
=  150,  which  may  be  taken  as  the  average  difference  between  the 
temperature  of  the  steam  and  the  air  of  the  room,  in  ordinary  low- 
pressure  work.  Taking  the  above  results,  we  have  150  X  1 .7  =  255 
B.  T.  U.  as  the  efficiency  of  an  average  cast-iron  or  pipe  radiator. 
This,  for  convenient  use,  may  be  taken  as  250.  A  circulation  coil 
made  up  of  pipes  from  1  to  2  inches  in  diameter,  will  easily  give  off 
300  B.  T.  U.  under  the  same  conditions;  and  a  cast-iron  wall  radiator 
with  ample  space  back  of  it  should  have  an  efficiency  equal  to  that 
of  a  wall  coil.  While  overhead  coils  have  a  higher  efficiency  than 
cast-iron  radiators,  their  position  near  the  ceiling  reduces  their  effec- 
tiveness, so  that  in  practice  the  efficiency  should  not  be  taken  over 
250  B.  T.  U.  per  hour  at  the  most.  Tabulating  the  above  we  have: 

TABLE   XIII 
Efficiency  of  Radiators,  Coils,  etc. 

TYPE  OF  RADIATING  SURFACE  RADIATION  PER  SQUARE  FOOT  OF  SURFACE 

PER  HOUR 


Cast-Iron  Sectional  and  Pipe  Radiators 
\Yall  Radiators 
Ceiling  Coils 
Wall  Coils 


250  B.  T.  U. 

300 

200  to  250         " 

300 


243 


48  HEATING  AND  VENTILATION 

If  the  radiator  is  for  warming  a  room  which  is  to  be  kept  at  a 
temperature  above  or  below  70  degrees,  or  if  the  steam  pressure  is 
greater  than  3  pounds,  the  radiating  surface  may  be  changed  in  the 
same  proportion  as  the  difference  in  temperature  between  the  steam 
and  the  air. 

For  example,  if  a  room  is  to  be  kept  at  a  temperature  of  00°,  the 
efficiency  of  the  radiator  becomes  -j^-  X  250  =  268;  that  is,  the 
efficiency  varies  directly  as  the  difference  in  temperature  between  the 
steam  and  the  air  of  the  room.  It  is  not  customary  to  consider  this 
unless  the  steam  pressure  should  be  raised  to  10  or  15  pounds  or  the 
temperature  of  the  rooms  changed  15  or  20  degrees  from  the  normal. 

From  the  above  it  is  easy  to  compute  the  size  of  radiator  for  any 
given  room.  First  compute  the  heat  loss  per  hour  by  conduction  and 
leakage  in  the  coldest  weather;  then  divide  the  result  by  the  effi- 
ciency of  the  type  of  radiator  to  be  used.  It  is  customary  to  make  the 
radiators  of  such  size  that  they  will  warm  the  rooms  to  70  degrees  in 
the  coldest  weather.  As  the  low-temperature  limit  varies  a  good  deal 
in  different  localities,  even  in  the  same  State,  the  lowest  temperature 
for  which  we  wish  to  provide  must  be  settled  upon  before  any  calcu- 
lations are  made.  In  Xew  England  and  through  the  Middle  and 
Western  States,  it  is  usual  to  figure  on  warming  a  building  to  70 
degrees  when  the  outside  temperature  is  from  zero  to  10  degrees 
below. 

The  different  makers  of  radiators  publish  in  their  catalogues, 
tables  giving  the  square  feet  of  heating  surface  for  different  styles  and 
heights,  and  these  can  be  used  in  determining  the  number  of  sections 
required  for  all  special  cases. 

If  pipe  coils  are  to  be  used,  it  becomes  necessary  to  reduce  square 
feet  of  heating  surface  to  linear  feet  of  pipe;  this  can  be  done  by  means 
of  the  factors  o-iven  below. 

=  linear  ft.  of  1  -in.  pipe 
Square  feet  of  heating  surf  ice  X  -{    ~"  „         t( 

"      2  -in.       " 

The  size  of  radiator  is  made  only  sufficient  to  keep  the  room 
warm  after  it  is  once  heated ;  and  no  allowance  is  made  for  warming 
up;  that  is,  the  heat  given  off  by  the  radiator  is  just  equal  to  that  lost 
through  walls  and.  windows.  This  condition  is  offset  in  two  ways — • 


244 


HEATING  AND  VENTILATION  49 

first,  when  the  room  is  cold,  the  difference  in  temperature  between 
the  steam  and  the  air  of  the  room  is  greater,  and  the  radiator  is  more 
efficient;  and  second,  the  radiator  is  proportioned  for  the  coldest 
weather,  so  that  for  a  greater  part  of  the  time  it  is  larger  than  neces- 
sary. 

EXAMPLES   FOR   PRACTICE 

1 .  The  heat  loss  from  a  room  is  25,000  B.  T.  U.  per  hour  in 
the  coldest  weather.     What  size  of  direct  radiator  will  be  required? 

ANS.  100  square  feet. 

2.  A  schoolroom  is  to  be  warmed  with  circulation  coils  of  1|- 
inch  pipe.    The  heat  loss  is  30,000  B.  T.  U.  per  hour.    What  length 
of  pipe  will  be  required?  ANS.  230  linear  feet. 

Location  of  Radiators.  Radiators  should,  if  possible,  be  placed 
in  the  coldest  part  of  the  room,  as  under  windows  or  near  outside 
doors.  In  living  rooms  it  is  often  desirable  to  keep  the  windows  free, 
in  which  case  the  radiators  may  be  placed  at  one  side.  Circulation 
coils  are  run  along  the  outside  walls  of  a  room  under  the  windows, 
Sometimes  the  position  of  the  radiators  is  decided  by  the  necessary 
location  of  the  pipe  risers,  so  that  a  certain  amount  of  judgment  must 
be  used  in  each  special  case  as  to  the  best  arrangement  to  suit  all 
requirements. 

Systems  of  Piping.  There  are  three  distinct  systems  of  piping, 
knowrn  as  the  two-pipe  system,  the  one-pipe  relief  system,  and  the  one- 
pipe  circuit  system,  with  various  modifications  of  each  and  combina- 
tions of  the  different  systems. 

Fig.  23  shows  the  arrangement  of  piping  and  radiators  in  the 
two-pipe  system.  The  steam  main  leads  from  the  top  of  the  boiler, 
and  the  branches  are  carried  along  near  the  basement  ceiling.  Risers 
are  taken  from  the  supply  branches,  and  carried  up  to  the  radiators 
on  the  different  floors;  and  return  pipes  are  brought  down  to  the 
return  mains,  which  should  be  placed  near  the  basement  floor  below 
the  water-line  of  the  boiler.  Where  the  building  is  more  than  two 
stories  high,  radiators  in  similar  positions  on  different  floors  are  con- 
nected with  the  same  riser,  which  may  run  to  the  highest  floor;  and  a 
corresponding  return  drop  connecting  with  each  radiator  is  carried 
down  beside  the  riser  to  the  basement.  A  system  in  which  the  main 
horizontal  returns  are  below  the  water-line  of  the  boiler  is  said  to 


245 


HEATING  AND  VENTILATION 


have  a  wet  or  sealed  return.  If  the  returns  are  overhead  and  above  the 
water-line,  it  is  called  a  dry  return.  Where  the  steam  is  exposed  to 
extended  surfaces  of  water,  as  in  overhead  returns,  where  the  con- 
densation partially  fills  the  pipes,  there  is  likely  to  be  cracking  or 
water-hammer,  due  to  the  sudden  condensation  of  the  steam  as  it 
comes  in  contact  with  the  cooler  water.  This  is  especially  noticeable 
when  steam  is  first  turned  into  cold  pipes  and  radiators,  and  the  con- 
densation is  excessive.  When  dry  returns  are  used,  the  pipes  should 
be  large  and  have  a  good  pitch  toward  the  boiler. 

In  the  case  of  sealed  returns,  the  onlv  contact  between  the  steam 


Fig.  23.    Arrangement  of  Piping  and  Radiators  in  "Two-Pipe"  System. 

and  standing  water  is  in  the  vertical  returns,  where  the  exposed  sur- 
faces are  very  small  (being  equal  to  the  sectional  area  of  the  pipes), 
and  trouble  from  water-hammer  is  practically  done  away  with.  Dry 
returns  should  be  given  an  incline  of  at  least  1  inch  in  10  feet,  while 
for  wet  returns  1  inch  in  20  or  even  40  feet  is  ample.  The  ends  of  all 
steam  mains  and  branches  should  be  dripped  into  the  returns.  If  the 
return  is  sealed,  the  drip  maybe  directly  connected  as  shown  in  Fig. 
24 ;  but  if  it  is  dry,  the  connection  should  be  provided  with  a  siphon 
loop  as  indicated  in  Fig.  25.  The  loop  becomes  filled  with  water, 
and  prevents  steam  from  flowing  directly  into  the  return.  As  the 


246 


HEATING  AND  VENTILATION 


condensation  collects  in  the  loop,  it  overflows  into  the  return  pipe  and 
is  carried  away.  The  return  pipes  in  this  case  are  of  course  filled  with 
steam  above  the  water;  but  it  is  steam  which  has  passed  through 
the  radiators  and  their  return  connections,  and  is  therefore  at  a 
slightly  lower  pressure;  steam  Marn 

so  that,  if  steam  were  ad- 
mitted directly  from  the 
main,  it  would  tend  to 
hold  back  the  water  in 

Wate- 

more  distant  returns  and 

cause  surging  and  crack-  Retxir-n 

ing  in  the  pipes.      Some-       Fig.  24.    Drip  from  Steam  Main  Connected  Directly 

times  the  boiler  is  at  a  to  sealed  Return. 

lower  level  than  the  basement  in  which  the  returns  are  run,  and  it  then 
becomes  necessary  to  establish  a  false  water-line.  This  is  done  by 
making  connections  as  shown  in  Fig.  26. 

It  is  readily  seen  that  the  return  water,  in  order  to  reach  the 
boiler,  must  flow  through  the  trap,  which  raises  the  water-line  or 
seal  to  the  level  shown  by  the  dotted  line.  The  balance  pipe  is  to 
equalize  the  pressure  above  and  below  the  water  in  the  trap,  and 
prevent  siphonic  action,  which  would  tend  to  drain  the  water  out  of 
the  return  mains  after  a  flow  was  once  started. 

The  balance  pipe,  when  possible,  should  be  15  or  20  feet  in 
length,  with  a  throttle-valve  placed  near  its  connection  with  the 

main.  This  valve 
should  be  opened  just 
enough  to  allow  the 
steam-pressure  to  act 
upon  the  air  which  oc- 
cupies the  space  above 
the  water  in  the  trap ; 
but  it  should  not  be 


SipVior* 


Fig.  25.    Use  of  Siphon  in  Connecting  Drip  from  Steam 
Main  to  a  "Dry"  Return. 


opened  sufficiently  to 
allow  the  steam  to 
enter  in  large  volume  and  drive  the  air  out.  The  success  of  this 
arrangement  depends  upon  keeping  a  layer  or  cushion  of  cool  air 
next  to  the  surface  of  the  water  in  the  trap,  and  this  is  easily  done 
by  following  the  method  here  described. 


247 


52 


HEATING  AND  VENTILATION 


Water-lirie 


One=Pipe  Relief  System.  In  this  system  of  piping,  the  radiators 
have  but  a  single  connection,  the  steam  flowing  in  and  the  condensa- 
tion draining  out  through  the  same  pipe.  Fig.  27  shows  the  method 
of  running  the  pipes  for  this  system.  The  steam  main,  as  before, 
leads  from  the  top  of  the  boiler,  and  is  carried  to  as  high  a  point  as  the 
basement  ceiling  will  allow;  it  then  slopes  downward  with  a  grade 
of  about  1  inch  in  10  feet,  and  makes  a  circuit  of  the  building  or  a 
portion  of  it. 

Risers  are  taken  from  the  top  and  carried  to  the  radiators  above, 
as  in  the  two-pipe  system;  but  in  this  case,  the  condensation  flows 
back  through  the  same  pipe,  and  drains  into  the  return  main  near  the 

floor  through 
drip  connections 
which  are  made 
at  frequent  in- 
tervals. In  a 
two-story  build- 
ing, the  bottom 
of,  each  riser  to 
the  second  floor 
is  dripped;  and 
in  larger  build- 
ings, it  is  cus- 
tomary to  drip 
each  riser  that 
has  more  than 
one  radiator  con- 
nected with  it.  If  the  radiators  are  large  and  at  a  considerable  dis- 
tance from  the  next  riser,  it  is  better  to  make  a  drip  connection  for 
each  radiator.  "When  the  return-  main  is  overhead,  the  risers  should 
be  dripped  through  siphon  loops;  but  the  ends  of  the  branches 
should  make  direct  connection  with  the  returns.  This  is  the  reverse 
of  the  two-pipe  system.  In  this  case  the  lowest  pressure  is  at  the 
ends  of  the  mains,  so  that  steam  introduced  into  the  returns  at  these 
points  will  cause  no  trouble  in  the  pipes  connecting  between  these  and 
the  boiler. 

If  no  steam  is  allowed  to  enter  the  returns,  a  vacuum  will  be 
formed,  and  there  will  be  no  pressure  to  force  the  water  back  to  the 


Boiler    '•'"• 

f. 

! 

i 

Fig.  26.     Connections  Made  to  Establish  "False"  Water-Lim 
when  Boiler  is  below  Basement  Level. 


248 


HEATING  AND  VENTILATION 


53 


boiler.     A  check-valve  should  always  be  placed  in  the  main  return 


Fig.  27.    Arrangement  of  Piping  and  Radiators  in  "One-Pipe  Relief"  System. 

near  the  boiler,  to  prevent  the  water  from  flowing  out  in  case  of 
vacuum  being  formed  suddenly  in  the  pipes. 


gementof  Piping  and  Radiators  in  "One-Pipe  Circuit"  System. 


There  is  but  little  difference  in  the  cost  of  the  two  systems,  as 
larger  pipes  and  valves  are  required  for  the  single-pipe  method. 


849 


HEATING  AND  VENTILATION 


\Vith  radiators  of  medium  size  and  properly  proportioned  connections, 
the  single-pipe  system  in  preferable,  there  being  but  one  valve  to 
operate  and  only  one-half  the  number  of  risers  passing  through  the 
lower  rooms. 

One=Pipe  Circuit  System.  In  this  case,  illustrated  in  Fig.  28,  the 
steam  main  rises  to  the  highest  point  of  the  basement,  as  before;  and 
then,  with  a  considerable  pitch,  makes  an  entire  circuit  of  the  build- 
ing, and  again  connects  with  the  boiler  below  the  water-line.  Single 

-          ___  _  _  risers   are  taken 


1  ^  l-^  — 

f—  '     M 

from  the  top;  and. 

the  condensa- 
tion drains  back 
through  the 

1                  1 

•n                    p 

1     Siphon 
ConrvecUo-n                        <jj 
•l>  in 

CV.ecV  Valve 
Connection^ 

is  carried  along 
with  the  flow  of 
steam  to  the  ex- 

rj                   tfj 

{_  }_  

*^  Sealed  Return 

Sealed  Ret  ^rn  f*^ 

main,  where  it  is 
returned  to  the 
b  o  i  1  e  r.  T  h  e 
main  is  made 

•- 

Fig.  29.     "One-Pipe  Circuit" 
Bui 

System.    Adapted  to  a  Large 

ding. 

large,  and  of 
the  same  size 

throughout  its  entire  length.  It  must  be  given  a  good  pitch  to  insure 
satisfactory  results. 

(  )ne  objection  to  a  single-pipe  system  is  that  the  steam  and  return 
water  are  flowing  in  opposite  directions,  and  the  risers  must  be  made 
of  extra  large  size  to  prevent  any  interference.  This  is  overcome  in 
large  buildings  by  carrying  a  single  riser  to  the  attic,  large  enough 
to  supply  the  entire  building;  then  branching  and  running  "drops" 
to  the  basement.  In  this  system  the  flow  of  steam  is  downward,  as 
well  as  that  of  water.  This  method  of  piping  may  be  used  with  good 
results  in  two-pipe  systems  as  well.  Care  must  always  be  taken  that 
no  pockets  or  low  points  occur  in  any  of  the  lines  of  pipe;  but  if  for 
any  reason  they  cannot  be  avoided,  they  should  be  carefully  drained. 

A  modification  of  this  system,  adapting  it  to  large  buildings,  is 
shown  in  diagram  in  Fig.  29.  The  riser  shown  in  this  case  is  one  of 


250 


ROCOCO    ORNAMENTAL    TriREE    COLUMN    PATTERN    RADIATOR    FOB 
WARMING    BY    HOT    WATER. 

American  Radiator  Company. 


HEATING  AND  VENTILATION 


55 


several,  the  number  depending  upon  the  size  of  the  building;  and 
may  be  supplied  at  either  bottom  or  top  as  most  desirable.  If  steam 
is  supplied  at  the  bottom  of  the  riser,  as  shown  in  the  cut,  all  of  the 
drip  connections  with  the  return  drop,  except  the  upper  one,  should 


Fig.  30.    "Two- Pipe"  Connection  of  Radia- 
tor to  Riser  and  Return. 


Pig.  31. 


'One-Pipe"  Connection  of  Radia- 
tor to  Basement  Main. 


be  sealed  with  either  a  siphon  loop  or  a  check-valve,  to  prevent  the 
steam  from  short-circuiting  and  holding  back  the  condensation  in  the 
returns  above.  If  an  overhead  supply  is  .used,  the  arrangement 
should  be  the  reverse;  that  is,  all  return  connections  should  be  sealed 
except  the  lowest. 

Sometimes  a  separate  drip  is  carried  down  from  each  set  of 
radiators,  as  shown  on  the  lower  story,  being  connected  with  the 
main  return  below  the  water-line  of  the 
boiler.     In  case  this  is  done,  it  is  well  to 
provide  a  check-valve  in  each  drip  below 
the  water-line. 

In  buildings  of  any  considerable  size, 
it  is  well  fo  divide  the  piping  system  into 
sections  by  means  of  valves  placed  in  the 
corresponding  supply  and  return  branches. 
These  are  for  use  in  case  of  a  break  in 
any  part  of  the  system,  so  that  it  will  be 
necessary  to  shut  off  only  a  small  part  of 
the  heating  system  during  repairs.  In  tall  buildings,  it  is  customary 
to  place  valves  at  the  top  and  bottom  of  each  riser,  for  the  same 
purpose. 

Radiator  Connections.    Figs.  30,  31,  and  32  show  the  common 


Fig.  32.    "One-Pipe"  Connection 
of  Radiator  to  Riser. 


251 


56  HEATIXG  AND  VENTILATION 


methods  of  making  connections  between  supply  pipes  and  radiators. 
Fig.  30  shows  a  two-pipe  connection  with  a  riser;  the  return  is  carried 
down  to  the  main  below.  Fig.  31  shows  a  smgle-pipe  connection 
with  a  basement  main;  and  Fig.  32,  a  single  connection  with  a  riser. 

Care  must  always  be  taken  to  make  the  horizontal  part  of  the 
piping  between  the  radiator  and  riser  as  short  as  possible,  and  to  give 
it  a  good  pitch  toward  the  riser.  There  are  various  ways  of  making 
these  connections,  especially  suited  to  different  conditions;  but  the 
examples  given  serve  to  show  the  general  principle  to  be  followed. 

Figs.  20,  21,  and  22  show  the  common  methods  of  making  steam 
and  return  connections  with  circulation  coils.  The  position  of  the 
air-valve  is  shown  in  each  case. 

Expansion  of  Pipes.     Cold  steam  pipes  expand  approximately 


Fig.  33.     Elevation  and  Plan  of  Swivel-Joint  to  Counteract  Effects  of  Expansion  and 
Contraction  in  Pipes. 

1  inch  in  each  100  feet  in  length  when  low-pressure  steam  is  turned 
into  them ;  so  that,  in  laying  out  a  system  of  piping,  we  must  arrange 
it  in  such  a  manner  that  there  will  be  sufficient  "spring"  or  "give"  to 
the  pipes  to  prevent  injurious  strains.  This  is  done  by  means  of  off- 
sets and  bends.  In  the  case  of  larger  pipes  this  simple  method  will 
not  be  sufficient,  and  swivel  or  slip  joints  must  be  used  to  take  up  the 
expansion. 

The  method  of  making  up  a  swivel-joint  is  shown  in  Fig.  33. 
Any  lengthening  of  the  pipe  A  will  be  taken  up  by  slight  turning  or 
swivel  movements  at  the  points  B  and  C.  A  slip-joint  is  shown  in 


252 


HEATING  AND  VENTILATION 


5? 


Fig.  34.  The  part  c  slides  inside  the  shell  d,  and  is  made  steam- 
tight  by  a  stuffing-box,  as  shown.  The  pipes  are  connected  at  the 
flanges  A  and  B. 
When  pipes 
pass  through 

d       I  C 


Q 


Fig.  34.    "Slip-Jotat"  Connection  to  Take  Care  of  Expansion 
and  Contraction  of  Pipes. 


floors    or    parti- 

tions,  the  wood- 

work should  be 

protected  by  gal- 

vanized-iron 

sleeves  having  a 

diameter  from  f  to  1  inch  greater  than  the  pipe.  Fig.  35  shows  a 

form  of  adjustable  floor-sleeve 
which  may  be  lengthened  or 
shortened  to  conform  to  the 
thickness  of  floor  or  partition. 
If  plain  sleeves  are  used,  a 
plate  should  be  placed  around 


L  -    ""'•  Fig.  36.    Floor-Plate  Adjusted  to  Plain 

Fig.  35.    Adjustable  Metal  Sleeve  for  Carrying  Sleeve  for  Carrying  Pipe  through 

Pipe  through  Floor  or  Partition.  Floor  or  Partition. 

the  pipe  where  it  passes  through  the  floor  or  partition.     These  are 


Fig.  37.    Angle  Valve. 


Fig.  38.    Offset  Valve.  Fig.  39.    Corner  Valve. 

Valves  for  Radiator  Connections. 


made  in  two  parts  so  that  they  may  be  put  in  place  after  the  pipe  is 
hung.     A  plate  of  this  kind  is  shown  in  Fig.  36. 


253 


HEATING  AND  VENTILATION 


Valves.  The  different  styles  commonly  used  for  radiator  con- 
nections are  shown  in  Figs.  37,  38,  and  39,  and  are  known  as  angle, 
offset,  and  corner  valves,  respectively.  The  first  is  used  when  the 
radiator  is  at  the  top  of  a  riser  or  when  the  connections  are  like  those 
shown  in  Figs.  30,  31,  and  32;  the  second  is  used  when  the  connection 


Fit:.  40.    Indicating  Effect  of  Using  Globe  Valve  on  Horizontal  Steam  Supply 
Pipe  or  Dry  Return. 

between  the  riser  and  radiator  is  above  the  floor;  and  the  third,  when 
the  radiator  has  to  be  set  close  in  the  corner  of  a  room  and  there  is  not 
space  for  the  usual  connection. 

A  globe  valve  should  never  be  used  in  a  horizontal  steam  supply 
or  dry  return.  The  reason  for  this  is  plainly 
shown  in  Fig.  40.  In  order  for  water  to  flow 
through  the  valve,  it  must  rise  to  a  height 
shown  by  the  dotted  line,  which  would  half 
fill  the  pipes,  and  cause  serious  trouble  from 
water-hammer.  The  gate  valve  shown  in 
Fig.  41  does  not  have  this  undesirable  fea- 
ture, as  the  opening  is  on  a  level  with  the 
bottom  of  the  pipe. 


Fig.  41.    Gate  Valve.  Fig.  42.    Simplest  Form  of  Air-Valve.    Operated  by  Hand. 

Air=Valves.  Valves  of  various  kinds  are  used  for  freeing  the 
radiators  from  air  when  steam  is  turned  on.  Fig.  42  shows  the 
simplest  form,  which  is  operated  by  hand.  Fig.  43  is  a  type  of  auto- 
matic valve,  consisting  of  a  shell,  which  is  attached  to  the  radiator. 
E  >s  a  small  opening  which  may  be  closed  by  the  spindle  C,  which 


254 


HEATING  AND  VENTILATION 


is  provided  with  a  conical  end.  D  is  a  strip  composed  of  a  layer  of 
iron  or  steel  and  one  of  brass  soldered  or  brazed  together.  The 
action  of  the  valve  is  as  follows : 
when  the  radiator  is  cold  and  filled 
with  air  the  valve  stands  as  shown 
in  the  cut.  When  steam  is  turned 
on,  the  air  is  driven  out  through 
the  opening  B.  As  soon  as  this 
is  expelled  and  steam  strikes  the 
strip  D,  the  two  prongs  spring 
apart  owing  to  the  unequal  ex- 
pansion of  the  two  metals  due  to 
the  heat  of  the  steam.  This 
raises  the  spindle  C,  and  closes 
the  opening  so  that  no  steam  can 
escape.  If  air  should  collect  in 
the  valve,  and  the  metal  strip 
become  cool,  it  would  contract, 
and  the  spindle  would  drop  and 
allow  the  air  to  escape  through  B 

as  before.  E  is  an  adjusting  nut.  F  is  a  float  attached  to  the  spindle, 
and  is  supposed,  in  case  of  a  sudden  rush 
of  water  with  the  air,  to  rise  and  close  the 
opening;  this  action,  however,  is  some- 
what uncertain,  especially  if  the  pressure 
of  water  continues  for  some  time. 

There  are  other  types  of  valves  acting 
on  the  same  principle.     The  valve  shown 


Fig.  43.      Radiator  Automatic  Air- Valve. 

Operated  by  Metal  Strip  />,  Consisting 

of  Two  Pieces  of  Metal  of  Unequal 

Expansive  Power. 


Fig.  44.    Automatic  Air- Valve.    Closed  by  Expansion 
of  a  Piece  of  Vulcanite. 


j.  45.     Automatic  Air- Valve, 
srated  by   Expansion  of 
•rum  <7Due  to  Vaporiza- 
tion of  Alcohol  with 
which  It  is  Partly 
Filled. 


in  Fig.  44  is  closed  by  the  expansion  of  a  piece  of  vulcanite  instead 
of  a  metal  strip,  and  has  no  water  float. 


255 


60 


HEATING  AND  VENTILATION 


The  valve  shown  in  Fig.  45  acts  on  a  somewhat  different  prin- 
ciple. The  float  C  is  made  of  thin  brass,  closed  at  top  and  bottom, 
and  is  partially  filled  with  wood  alcohol.  When  steam  strikes  the 
float,  the  alcohol  is  vaporized,  and  creates  a  pressure  sufficient  to 
bulge  out  the  ends  slightly,  which  raises  the  spindle  and  closes  the 
opening  B. 

Fig.  4(J  shows  a  form  of  so-called  vacuum  valve.  It  acts  in  a 
similar  manner  to  those  already  described,  but  has  in  addition  a 
ball  check  which  prevents  the  air  'from  being 
drawn  into  the  radiator,  should  the  steam  go 
down  and  a  vacuum  be  formed.  If  a  partial 
vacuum  exists  in  the  boiler  and  radiators,  the 
boiling  point,  and  consequently  the  tempera- 
ture of  the  steam,  are  lowered,  and  less  heal  is 
given  off  by  the  radiators.  This  method  of 
operating  a  heating  plant  is  sometimes  advo- 
cated for  spring  and  fall,  when  little  heat  is  re- 
quired, and  when  steam  under  pressure  would 
overheat  the  rooms. 

Pipe  Sizes.  The  proportioning  of  the  steam 
pipes  in  a  heating  plant  is  of  the  greatest  im- 
portance, and  should  be  carefully  worked  out 
by  methods  which  experience  has  proved  to  be 
correct.  There  are  several  ways  of  doing  this; 
but  for  ordinary  conditions,  Tables  XIV,  XV, 
and  XVI  have  given  excellent  results  in  actual  practice.  They 
have  been  computed  from  what  is  known  as  D'Arcy's  formula,  with 
suitable  corrections  made  for  actual  working  conditions.  As  the 
computations  are  somewhat  complicated,  only  the  results  will  be  given 
here,  with  full  directions  for  their  proper  use. 

Table  XIV  gives  the  flow  of  steam  in  pounds  per  minute  for 
pipes  of  different  diameters  and  with  varying  drops  in  pressure  be- 
tween the  supply  and  discharge  ends  of  the  pipe.  These  quantities 
are  for  pipes  100  feet  in  length;  for  other  lengths  the  results  must  be 
corrected  by  the  factors  given  in  Table  XVI.  As  the  length  of  pipe 
increases,  friction  becomes  greater,  and  the  quantity  of  steam  dis- 
charged in  a  given  time  is  diminished. 

Table  XIV  is  computed  on  the  assumption  that  the  drop  in 


Fig.  46.    Vacuum  Valve 


HEATING  AND  VENTILATION 


(11 


TABLE   XIV 

Flow  of  Steam  in  Pipes  of  Various  Sizes,  with  Various  Drops  in  Pres- 
sure between  Supply  and  discharge  Ends 

Calculated  for  100-Foot  Lengths  of  Pipe 


DROP  IN  PRESSURE  (POUNDS) 


ft"1 

M 

X 

M 

1 

iy2 

2 

3 

4 

5 

l 

.44 

.63 

.78 

91 

1.13 

1.31 

1.66 

1.97 

2.26 

1/4 

.81 

1.16 

1.43 

1.66 

2.05 

2.39 

3.02 

3.59 

4.12 

iy2 

1.06 

1.89 

2.34 

2.71 

3.36 

3.92 

4.94 

5.88 

6.75 

2 

2.93 

4.17 

5.16 

5.99 

7.43 

8.65 

10.9 

13.0 

14.9 

2% 

5.29 

7.52 

9.32 

10.8 

13.4 

15.6 

19.7 

23  A 

26.9 

3 

8.61 

12.3 

15.2 

17.6 

21.8 

25.4 

32 

31.8 

43.7 

;  ;  i  .; 

12.9 

18.3 

22.'6 

26.3 

32.5 

37.9 

47.8 

56.9 

65.3 

4 

18  1 

25.7 

31.8 

36.9 

45.8 

53.3 

67.2 

80.1 

91.9 

5 

32.2 

45.7 

56.6 

65.7 

.  81.3 

94.7 

120 

142 

163 

6 

51.7 

73.3 

90.9 

106 

131 

152 

192 

229 

262 

7 

76.7 

109 

135 

157 

194 

226 

285 

339 

390 

8 

108 

154 

190 

222 

274 

319 

402 

478 

549 

9 

147 

209 

258 

299 

371 

432 

545 

649 

745 

0 

192 

273 

339 

393 

487 

567 

715 

852 

977 

2 

305 

434 

537 

623 

771 

899 

1,130 

1,350 

1,550 

5 

535 

761 

942 

1,090 

1,350 

1,580 

1,990 

2,370 

2,720 

pressure  between  the  two  ends  of  the  pipe  equals  the  initial  pressure. 
If  the  drop  in  pressure  is  less  than  the  initial  pressure,  the  actual 
discharge  will  be  slightly  greater  than  the  quantities  given  in  the  table; 

TABLE   XV 

Factors  for  Calculating  Flow  of  Steam   in  Pipes  under    Initial    Pres- 
sures above  Five  Pounds 

To  be  used  in  connection  with  Table  XIV 


DROP  IN* 

I 

NITIAL  PRESS 

URE  (POUNDS 

) 

N  POUNDS 

10 

20 

30 

40 

60 

80 

J 

1.27 

1.49 

1.68 

1.84 

2.13 

2.38 

| 

1.26 

1.48 

1.66 

.83 

2.11 

2.36 

1 

.24 

1.46 

1.64 

.80 

2.08 

2.32 

2 

.21 

1.41 

1.59 

.75 

2.02 

2.26 

3 

.17 

1.37 

1.55 

.70 

1.97 

2.20 

4 

.14 

1.34 

1.51 

.66 

1.92 

2.14 

5 

.12 

1.31 

1.47 

.62 

1.87. 

2.09 

but  this  difference  will  be  small  for  pressures  up  to  5  pounds,  and  may 
be  neglected,  as  it  is  on  the  side  of  safety.  For  higher  initial  pressures, 
Table  XV  has  been  prepared.  This  is  to  be  used  in  connection  with 
Table  XIV  as  follows :  First  find  from  Table  XIV  the  quantity  of 
steam  which  will  be  discharged  through  the  given  diameter  of  pipe 


257 


02  HEATING  AND  VENTILATION 


TABLE   XVI 

Factors    for  Calculating   Flow  of    Steam   in    Pipes  of    Other   Lengths 
than    100   Feet 


10 

316 

120 

.91 

275 

.60 

600 

.40 

20 

2.24 

130 

.87 

300 

.  o/ 

650 

.  39 

30 

1.82 

140 

.84 

325 

.  55 

700 

.37 

40 

1.58 

150 

.81 

350 

.53 

750 

.36 

50 

1.41 

160 

.79 

375 

.51 

800 

.  35 

60 

1.29 

170 

.76 

400 

.50 

850 

.34 

70 

1.20 

180 

.74 

425 

.48 

900 

.33 

80 

1.12 

190 

72 

450 

.47 

950 

.32 

90 

1.05 

200 

.70 

475 

.46 

1,000 

.31 

100 

1  .  00 

225 

.66 

500 

.45 

110 

.95 

250 

.63 

550 

.42 

with  the  assumed  drop  in  pressure;  then  look  in  Table  XV  for  the 
factor  corresponding  with  the  assumed  drop  and  the  higher  initial 
pressure  to  be  used.  The  quantity  given  in  Table  XIV,  multiplied 
by  this  factor,  will  give  the  actual  capacity  of  the  pipe  under  the  given 
conditions. 

Example — What  weight  of  steam  will  be  discharged  through  a  3-inch 
pipe  100  feet  long,  with  an  initial  pressure  of  60  pounds  and  a  drop  of  2  pounds? 

Looking  in  Table  XIV,  we  find  that  a  3-inch  pipe  will  dis- 
charge 25 . 4  pounds  of  steam  per  minute  with  a  2-pound  drop.  Then 
looking  in  Table  XV,  we  find  the  factor  corresponding  to  GO  pounds 
initial  pressure  and  a  drop  of  2  pounds  to  be  2.02.  Then  according 
to  the  rule  given,  25.4  X  2.02  =  51 .3  pounds,  which  is  the  capacity 
of  a  3-inch  pipe  under  the  assumed  conditions. 

Sometimes  the  problem  will  be  presented  in  the  following  way: 
What  size  of  pipe  will  be  required  to  deliver  SO  pounds  of  steam  a 
distance  of  100  feet  with  an  initial  pressure  of  40  pounds  and  a  drop 
of  3  pounds? 

We  have  seen  that  the  higher  the  initial  pressure  with  a  given 
drop-,  the  greater  will  be  the  quantity  of  steam  discharged;  therefore 
a  smaller  pipe  will  be  required  to  deliver  80  pounds  of  steam  at  40 
pounds  than  at  3  pounds  initial  pressure  From  Table  XV,  we  find 
that  a  given  pipe  will  discharge  1 .7  times  as  much  steam  per  minute 
with  a  pressure  of  40  pounds  and  a  drop  of  3  pounds,  as  it  would  with 
a  pressure  of  3  pounds,  dropping  to  zero.  From  this  it  is  evident 
that  if  we  divide  SO  by  1 .7  and  look  in  Table  XIV  under  "3  pounds 


358 


HEATING  AND  VENTILATION  63 

drop"  for  the  result  thus  obtained,  the  size  of  pipe  corresponding  will 
be  that  required.  Now,  80  -r-  1 .7  =  47.  The  nearest  number  in  the 
table  marked  "3  pounds  drop"  is  47.8,  which  corresponds  to  a  3^- 
inch  pipe,  which  is  the  size  required. 

These  conditions  will  seldom  be  met  with  in  low-pressure  heating, 
but  apply  more  particularly  to  combination  power  and  heating  plants, 
and  will  be  taken  up  more  fully  under  that  head.  For  lengths  of 
pipe  other  than  100  feet,  multiply  the  quantities  given  in  Table  XIV 
by  the  factors  found  in  Table  XVI. 

Example — What  weight  of  steam  will  be  discharged  per  minute  through 
a  3£-inch  pipe  450  feet  long,  with  a  pressure  of  5  pounds  and  a  drop  of  £  pound? 

Table  XIV,  which  may  be  used  for  all  pressures  below  10  pounds, 
gives  for  a  3^-inch  pipe  100  feet  long,  a  capacity  of  18.3  pounds  for 
the  above  conditions.  Looking  in  Table  XVI,  we  find  the  correction 
factor  for  450  feet  to  be  .47.  Then  18.3  X  .47-8.6  pounds,  the 
quantity  of  steam  which  will  be  discharged  if  the  pipe  is  450  feet 

long- 
Examples  involving  the  use  of  Tables  XIV,  XV,  and  XVI  in 
combination,  are  quite  common  in  practice.     The  following  example 
will  show  the  method  of  calculation: 

What  size  of  pipe  will  be  required  to  deliver  90  pounds  of  steam  per 
minute  a  distance  of  800  feet,  with  an  initial  pressure  of  80  pounds  and  a  drop 
of  5  pounds? 

Table  XVI  gives  the  factor  for  800  feet  as  .35,  and  Table  XV, 
that  for  80 'pounds  pressure  and  5  pounds  drop,  as  2.09.  Then 

90 

—— - — ^-7.7.  =  123,  which  is  the  equivalent  quantity  we  must  look 
.  oo  X  2 . 09 

for  in  Table  XIV.  We  find  that  a  4-inch  pipe  will  discharge  91.9 
pounds,  and  a  5-inch  pipe  163  pounds.  A  4^-inch  pipe  is  not  com- 
monly carried  in  stock,  and  we  should  probably  use  a  5-inch  in  this 
case,  unless  it  was  decided  to  use  a  4-inch  and  allow  a  slightly  greater 
drop  in  pressure.  In  ordinary  heating  work,  with  pressures  varying 
from  2  to  5  pounds,  a  drop  of  \  pound  in  100  feet  has  been  found  to 
give  satisfactory  results. 

In  computing  the  pipe  sizes  for  a  heating  system  by  the  above 
methods,  it  would  be  a  long  process  to  work  out  the  size  of  each 
branch  separately.  Accordingly  Table  XVII  has  been  prepared  for 
ready  use  in  low-pressure  work. 


259 


(11 


HEATING  AND  VENTILATION 


As  most  direct  heating  systems,  and  especially  those  in  school- 
houses,  are  made  up  of  both  radiators  and  circulation  coils,  an  effi- 
ciency of  300  B.  T.  U.  has  been  taken  for  direct  radiation  of  whatever 
variety,  no  distinction  being  made  between  the  different  kinds.  This 
gives  a  slightly  larger  pipe  than  is  necessary  for  cast-iron  radiators; 
but  it  is  probably  offset  by  bends  in  the  pipes,  and  in  any  case  gives  a 
slight  factor  of  safety.  We  find  from  a  steam  table  that  the  latent 
heat  of  steam  at  20  pounds  above  a  vacuum  (which  corresponds  to 
5  pounds' gauge-pressure)  is  954  +  B.  T.  U. — which  means  that,  for 
every  pound  of  steam  condensed  in  a  radiator,  9o4  B.  T.  U.  are  given 
off  for  warming  the  air  of  the  room.  If  a  radiator  has  an  efficiency 
of  300  B.  T.  U.,  then  each  square  foot  of  surface  will  condense  300  H- 
9.">4  =  .314  pound  of  steam  per  hour;  so  that  we  may  assume  in 
round  numbers  a  condensation  of  \  of  a  pound  of  steam  per  hour  for 
each  square  foot  of  direct  radiation,  when  computing  the  sizes  of 
steam  pipes  in  low-pressure  heating.  Table  XVII  has  been  calculated 
on  this  assumption,  and  gives  the  square  feet  of  heating  surface 

TABLE  XVI! 

Heating  Surface  Supplied  by  Pipes  of  Various  Sizes 
Length  of  Pipe,   100  Feet 


SQUARK  FKKT  OF  HKATIXG  SURFACE 


\  Pound  Drop             J  Pound  Drop 

80 

114 

145 

210 

190 

340 

525 

750 

950 

1,350 

1.550 

2.210 

2,320 

3,290 

3,250 

4,620 

5,800 

8,220 

9.320 

13,200 

13.800 

19.020 

19.440               27.720 

which  different  sizes  of  pipe  will  supply,  with  drops  in  pressure  of 
\  and  ',  pounds  in  each  100  feet  of  pipe.  The  former  should  be  used 
for  pressures  from  1  to  5  pounds,  and  the  latter  may  be  used  for 
pressures  over  5  pounds,  under  ordinary  conditions.  The  sizes  of 
long  mains  and  special  pipes  of  large  size  should  be  proportioned 
directlv  from  Tables  XIV,  XV,  and  XVI. 


260 


HEATING  AND  VENTILATION 


Where  the  two-pipe  system  is  used  and  the  radiators  have  sepa- 
rate supply  and  return  pipes,  the  risers  or  vertical  pipes  may  be  taken 
from  Table  XVII;  but  if  the  single-pipe  system  is  used,  the  risers 
must  be  increased  in  size,  as  the  steam  and  water  are  flowing  in  oppo- 
site directions  and  must  have  plenty  of  room  to  pass  each  other.  It 
is  customary  in  this  case  to  base  the  computation  on  the  velocity  of 
the  steam  in  the  pipes,  rather  than  on  the  drop  in  pressure.  Assum- 
ing, as  before,  a  condensation  of  one-third  of  a  pound  of  steam  per 
hour  per  square  foot  of  radiation,  Tables  XVIII  and  XIX  have  been 
prepared  for  velocities  of  10  and  15  feet  per  second.  The  sizes  given 
in  Table  XIX  have  been  found  sufficient  in  most  cases ;  but  the  larger 
sizes,  based  on  a  flow  of  10  feet  per  second,  give  greater  safety  and 
should  be  more  generally  used.  The  size  of  the  largest  riser  should 
usually  be  limited  to  2^  inches  in  school  and  dwelling-house  work, 
unless  it  is  a  special  pipe  carried  up  in  a  concealed  position.  If  the 
length  of  riser  is  short  between  the  lowest  radiator  and  the  main,  a 
higher  velocity  of  20  feet  or  more  may  be  allowed  through  thjs  por- 
tion, rather  than  make  the  pipe  excessively  large. 

TABLE  XVIII  TABLE  XIX 

Radiating  Surface  Supplied  by  Steam  Risers 


1 0  FEET  PER  SECOND  VELOCITY 


15  FEET  PER  SECOND  VELOCITY 


Size  of  Pipe 

Sq.  Feet  of  Radiation 

Size  of  Pipe 

Sq.  Feet  of  Radiation 

1     in. 

30 

1     in. 

50 

H    ' 

60 

H  " 

90 

1?    ' 

80 

if" 

120 

2      ' 

130 

2     " 

200 

2J    ' 

190 

2J  " 

290 

3      ' 

290 

3     " 

340 

3*    ' 

390 

3J  " 

.      590 

EXAMPLES   FOR  PRACTICE 

1.  How  many  pounds  of  steam  will  be  delivered  per  minute, 
through  a  3^-inch  pipe  600  feet  long,  with  an  initial  pressure  of  5 
pounds  and  a  drop  of  |  pound?  ANS.  7.32  pounds. 

2.  What  size  pipe  will  be  required  to  deliver  25.52  pounds 
of  steam  per  minute  with  an  initial  pressure  of  3  pounds  and  a  drop 
of  j  pound,  the  length  of  the  pipe  being  50  feet?        ANS.  4-inch. 

3.  Compute  the  size  of  pipe  required  to  supply  10,000  square 
feet  of  direct  radiation  (assume  ^  of  a  pound  of  steam  per  square 


261 


66 


HEATING  AND  VENTILATION 


foot  per  hour)  where  the  distance  to  the  boiler  house  is  300  feet,  and 
the  pressure  carried  is  10  pounds,  allowing  a  drop  in  pressure  of 
4  pounds.  Axs.  5-inch  (this  is  slightly  larger  than  is  required,  while 
a  4-inch  is  much  too  small). 

TABLE  XX 
Sizes  of  Returns  for  Steam  Pipes   (in  Inches) 


DIAMETER  <n-  STEAM  PIPK          DIAMETER  OF  DRY  RETURN      DIAMKTER  OF  SEALED  RETURN 

1                                                          1 

1 

U                                   i 

1       - 

H                                   H 

1 

2 

H 

U 

24 

2 

14 

3" 

2* 

2" 

34 

.    24 

2 

4 

3 

24 

o 

3 

2* 

6 

3* 

3 

7 

34 

3 

8 

4 

34 

0                                              5 

34 

i  n                                   5 

4" 

12                                              6                                                5 

Returns.  The  size  of  return  pipes  is  usually  a  matter  of  custom 
and  judgment  rather  than  computation.  It  is  a  common  rule  among 
steamh'tters  to  make  the  returns  one  size  smaller  than  the  corre- 
sponding steam  pipes.  This  is  a  good  rule  for  the  smaller  sizes,  but 
gives  a  larger  return  than  is  necessary  for  the  larger  sizes  of  pipe. 
Table  XX  gives  different  sizes  of  steam  pipes  with  the  corresponding 
diameters  for  dry  and  sealed  returns. 

TABLE   XXI 
Pipe  Sizes  for  Radiator  Connections 


SQUARE  FEET  c 

E  RADIATION 

STEAM                               RETURN 

Two-Pipe 

10  to    30 
30  to    48 
48  to    96 
96  to  150 

f  inch                          f  inch 

1!  "•      i    i!  :  ' 

Single-Pipe 

10  to    24 
24  to    60 
60  to    80 

80  to  130 

i 

1     inch 
i 

i*  - 

I 

262 


HEATING  AND  VENTILATION 


67 


The  length  of  run  and  number  of  turns  in  a  return  pipe  should 
be  noted,  and  any  unusual  conditions  provided  for.  Where  the 
condensation  is  discharged  through  a  trap  into  a  lower  pressure,  the 
sizes  given  may  be  slightly  reduced,  especially  among  the  larger 
sizes,  depending  upon  the  differences  in  pressure. 

Radiators  are  usually  tapped  for  pipe  connections  as  shown  in 
Table  XXI,  and  these  sizes  may  be 
used  for  the  connections  with  the 
mains  or  risers. 

Boiler  Connections.  The  steam 
main  should  be  connected  to  the 
rear  nozzle,  if  a  tubular  boiler  is 
used,  as  the  boiling  of  the  water  is 
less  violent  at  this  point  and  dryer 
steam  will  be  obtained.  The  shut- 
off  valve  should  be  placed  in  such  a  position  that  pockets  for  the 
accumulation  of  condensation  will  be  avoided.  Fig.  47  shows  a  good 
position  for  the  valve. 

The  size  of  steam  connection  may  be  computed  by  means  of  the 
methods  already  given,  if  desired.  But  for  convenience  the  sizes 
given  in  Table  XXII  may  be  used  with  satisfactory  results  for  the 
short  runs  between  the  boilers  and  main  header. 


Fig  47.    Good  Position  for  Shut-Off 
Valve. 


TABLE  XXII 
Pipe  Sizes  from  Boiler  to  Main  Header 


DIAMETER  OF  BOILER 


SIZE  OF  STKAM 


36  inches 

3  inches 

42 

4 

48 

4 

54 

5 

60 

5 

66 

6 

72 

6 

The  return  connection  is  made  through  the  blow-off  pipe,  and 
should  be  arranged  so  that  the  boiler  can  be  blown  off  without  draining 
the  returns.  A  check- valve  should  be  placed  in  the  main  return,  and 
a  plug-cock  in  the  blow-off  pipe.  Fig.  48  shows  in  plan  a  good 
arrangement  for  these  connections. 


HEATING  AND  VEXTILATIOX 


The  feed  connections,  with  the  exception  of  that  part  exposed 
in  the  smoke-bonnet,  are  always  made  of  brass  in  the  best  class  of 
work.  The  small  section  referred  to  should  be  of  extra  heavv  wrought 


Fig.  48.     A  Good  Arran.uemem  of  Return  and  Rlow-Off  Connections. 

iron.  The  branch  to  each  boiler  should  be  provided  with  a  gate 
or  globe  valve  and  a  check-valve,  the  former  being  placed  next  to  the 
boiler. 

Table  XXIII  gives  suitable  sizes  for  return,  blow-off,  and  feed 
pipes  for  boilers  of  different  diameters. 

TABLE  XXIII 
Sizes  tor  Return,  Blow=Off,  and  Feed  Pipes 


DIAMETER   OF    Hoil 


SIZE  OF  PIPK  SIZE  OF  BLOW-OFF    j 

GRAVITY  KKTURN  PIPE 


MO  i  nolle* 

H  inches 

1  \  inches 

1 

inch 

j., 

9         '• 

H       '• 

1 

}s 

2 

H        ' 

1 

/H 

2i      " 

9            " 

H 

00 

2i          " 

9            " 

M 

" 

tiO 

3 

2t 

" 

"2 

3 

2i 

l* 

Blow=0ff  Tank.  Where  the  blow-off  pipe  connects  with  a 
sewer,  some  means  must  be  provided  for  cooling  the  water,  or  the 
expansion  and  contraction  caused  by  the  hot  water  flowing  through 
the  drain-pipes  will  start  the  joints  and  cause  leaks.  For  this  reason 
it  is  customary  to  pass  the  water  through  a  blow-off  tank.  A  form 
of  wrought-iron  tank  is  shown  in  Fig.  49.  It  consists  of  a  receiver 
supported  on  cast-iron  cradles.  The  tank  ordinarily  stands  nearly 
full  of  cold  water. 

The  pipe  from  the  boiler  enters  above  the  water-line,  and  the 
sewer  connection  leads  from  near  the  bottom,  as  shown.  A  vapor 
pipe  is  carried  from  the  top  of  the  tank  above  the  roof  of  the  building. 
When  water  from  the  boiler  is  blown  into  the  tank,  cold  water  from 


264 


HEATING  AND  VENTILATION 


the  bottom  flows  into  the  sewer,  and  the  steam  is  carried  off  through 
the  vapor  pipe.  The  equalizing  pipe  is  to  prevent  any  siphon  action 
which  might  draw  the  water  out  of  the  tank  after  a  flow  is  once  started. 
As  only  a  part  of  the  water  is  blown  out  of  a  boiler  at  one  time,  the 
blow-off  tank  can  be  of  a  comparatively  small  size.  A  tank  24  by  48 
inches  should  be  large  enough  for  boilers  up  to  48  inches  in  diameter; 


CQUAL/Z/MG 

PIPE 


FROM  BOILER 


WATER      LINE 


Fig.  49.    Connections  of  Blow-Off  Tank. 

and  one  36  by  72  inches  should  care  for  a  boiler  72  inches  in  diameter. 
If  smaller  quantities  of  water  are  blown  off  at  one  time,  smaller  tanks 
can  be  used.  The  sizes  given  above  are  sufficient  for  batteries  of  2  or 
more  boilers,  as  one  boiler  can  be  blown  off  and  the  water  allowed  to 
cool  before  a  second  one  is  blown  off.  Cast-iron  tanks  are  often 
used  in  place  of  wrought-iron,  and  these  may  be  sunk  in  the  ground 
if  desired. 


865 


Cast  Iron  Seamless  Tubular  Steam  Heater. 


HEATING  AND  VENTILATION 

PART  II 


INDIRECT  STEAM  HEATING 

As  already  stated,  in  the  indirect  method  of  steam  heating,  a 
special  form  of  heater  is  placed  beneath  the  floor,  and  encased  in 
galvanized  iron  or  in  brickwork.  A  cold-air  box  is  connected  with 
the  space  beneath  the  heater;  and  warm-air  pipes  at  the  top  are 
connected  with  registers  in  the  floors  or  walls  as  already  described  for 
furnaces.  A  separate  heater  may  be  provided  for  each  register  if  the 
rooms  are  large,  or  two  or  more  registers  may  be  connected  with  the 
same  heater  if  the  horizontal  runs  of  pipe  are  short.  Fig.  50  shows 
a  section  through  a  heater  arranged  for  introducing  hot  air  into  a 
room  through  a  floor  register;  and  Fig.  51  shows  the  same  type  of 
heater  connected  with  a  wall  register.  The  cold-air  box  is  seen  at 
the  bottom  of  the  casing;  and  the  air,  in  passing  through  the  spaces 
between  the  sections  of  the  heater,  becomes  warmed,  and  rises  to  the 
rooms  above. 

Different  forms  of  indirect  heaters  are  shown  in  Figs.  52  and  53. 
Several  sections  con- 
nected in  a  single  group        -^  __— ___^^^_ __  ._     = 

are  called  a  stack.  Some- 
times the  stacks  are  en- 
cased in  brickwork  built 
up  from  the  basement 
floor,  instead  of  in  gal- 
vanized iron  as  shown  in 
the  cuts.  This  method 
of  heating  provides  fresh 
air  for  ventilation, and  for 
this  reason  is  especially 

adapted  for  schoolhouses,  hospitals,  churches,  etc.  As  com- 
pared with  furnace  heating,  it  has  the  advantage  of  being  less 
affected  by  outside  wind-pressure,  as  long  runs  of  horizontal  pipe 


Fig.  50.    Steam  Heater  Placed  under  Floor  Register 
—Indirect  System. 


267 


HEATING  AND  VENTILATION 


are  avoided  and  the  heaters  can  be  placed  near  the  registers.     In  a 
large  building  where  several  furnaces  would  be  required,  a  single 

boiler  can  be  used,  and  the  num- 
ber of  stacks  increased  to  suit 
the  existing  conditions,  thus 
making  it  necessary  to  run  but 
a  single  fire.  Another  advan- 
tage is  the  large  ratio  between 
the  heating  and  grate  surface 
as  compared  with  a  furnace; 
and  as  a  result,  a  large  quan- 
tity of  air  is  warmed  to  a  mod- 
erate temperature,  in  place  of 
a  smaller  quantity  heated  to  a 
much  higher  temperature. 
This  gives  a  more  agreeable 
quality  to  the  air,  and  renders 
it  less  dry.  Direct  and  indi- 
rect systems  are  often  com- 
bined, thus  providing  the  liv- 
ing rooms  with  ventilation,  while  the  hallways,  corridors,  etc.,  have 
only  .direct  radiators  for  warming. 

Types  of  Heaters.  Various  forms  of  indirect  radiators  are  shown 
in  Figs.  52,  53,  54,  and  50.  A  hot-water  radiator  may  be  used  for 
steam;  but  a  steam  radiator  cannot  alwavs  be  used  for  hot  water,  as 


Fig.  51.    Steam  Heater  Conn 
ister.— Indirect  S 


.•ted  to  Wall  Reg- 
stem. 


Fig.  52.    One  Form  of  Indirect  Steam  or  Hot-Water  Heater. 

it  must  be  especially  designed  to  produce  a  continuous  flow  of  water 
through  it  from  top  to  bottom.  Figs.  54  and  55  show  the  outside 
and  the  interior  construction  of  a  common  pattern  of  indirect  radiator 


HEATING  AND  VENTILATION 


73 


designed  especially  for  steam.  The  arrows  in  Fig.  55  indicate  the 
path  of  the  steam  through  the  radiator,  which  is  supplied  at  the  right, 
while  the  return  connection  is  at  the  left.  The  air-valve  in  this  case 
should  he  connected  in  the  end  of  the  last  section  near  the  return. 


Fig.  53.    Another  Form  of  Indirect  Steam  or  Hot- Water  Heater. 

A  very  efficient  form  of  radiator,  and  one  that  is  especially  adapted 
to  the  warming  of  large  volumes  of  air,  as  in  schoolhouse  work,  is 
shown  in  Fig.  56,  and  is  known  as  the  School  pin  radiator.  This  can 


Fig.  54.    Exterior  View  of  a  Common  Type  of  Radiator  for  Indirect-Steam  Heating. 

be  used  for  either  steam  or  hot  water,  as  there  is  a  continuous  passage 
downward  from  the  supply  connection  at  the  top  to  the  return  at  the 
bottom.  These  sections  or  slabs  are  made  up  in  stacks  after  the 


Fig.  55.    Interior  Mechanism  of  Radiator  Shown  in  Fig.  54. 

manner  shown  in  Fig.  57,  which  represents  an  end  view  of  several 
sections  connected  together  with  special  nipples. 

A  very  efficient  form  of  indirect  heater  may  be  made  up  of 
wrought-iron  pipe  joined  together  with  branch  tees  and  return  bends. 


74 


HEATING  AND  VENTILATION 


A  heater  like  that  shown  in  Fig.  58  is  known  as  a  box  coil.  Its  effi- 
ciency is  increased  if  the  pipes  are  staggered — that  is,  if  the  pipes  in 
alternate  rows  are  placed  over  the  spaces  between  those  in  the  row 
below. 

Efficiency  of    Heaters.    The  efficiency  of    an  indirect    heater 


Fig.  50.    "School  Pin"  Radiator,  Especially  Adapted  for  Warming  Large  Volumes  of 
Air  by  Either  Steam  or  Hot  Water. 

depends  upon  its  form,  the  difference  in  temperature  between  the 
steam  and  the  surrounding  air,  and  the  velocity  with  which  the  air 
passes  over  the  heater.  Under  ordinary  conditions  in  dwelling-house 
work,  a  good  form  of  indirect  radiator  will  give  off  about  2  B.  T.  U. 
per  square  foot  per  hour  for 
each  degree  difference  in  tem- 
perature between  the  steam 
and  the  entering  air.  Assum- 
ing a  steam  pressure  of  2 
pounds  and  an  outside  tem- 
perature of  zero,  we  should 
have  a  difference  in  tempera- 
ture of  about  220  degrees, 
which,  under  the  conditions 
stated,  would  give  an  efficiency 
of  220  X  2  =  440  B.  T.  U. 
per  hour  for  each  square  foot 
of  radiation.  By  making  a  similar  computation  for  10  degrees  be- 
low zero,  we  find  the  efficiency  to  be  460.  In  the  same  manner  we 
may  calculate  the  efficiency  for  varying  conditions  of  steam  pressure 
and  outside  temperature.  In  the  case  of  schoolhouses  and  similar 
buildings  where  large  volumes  of  air  are  warmed  to  a  moderate  tem- 


Fig.  57.    End  View  of  Several  "School  Pin" 
Radiator  Sections  Connected  Together. 


270 


HEATING  AND  VENTILATION 


75 


perature,  a  somewhat  higher  efficiency  is  obtained,  owing  to  the  in- 
creased velocity  of  the  air  over  the  heaters.  Where  efficiencies  of  440 
and  460  are  used  for  dwellings,  we  may  substitute  600  and  620  for 
schoolhouses.  This  corresponds  approximately  to  2.7  B.  T.  U.  per 
square  foot  per  hour  for  a  difference  of  1  degree  between  the  air  and 
steam. 

The  principles  involved  in  indirect  steam  heating  are  sirhilar 
to  those  already  described  in  furnace  heating.  Part  of  the  heat  given 
off  by  the  radiator  must  be  used  in  warming  up  the  air-supply  to  the 
temperature  of  the  room,  and  part  for  offsetting  the  loss  by  conduction 
through  walls  and  windows.  The  method  of  computing  the  heating 
surface  required,  depends  upon  the  volume  of  air  to  be  supplied  to  the 
room.  In  the  case  of  a  schoolroom  or  hall,  where  the  air  quantity 


S/I3C    l//£~H/ 


1 

! 

i  r 
1  CD 

Fig,  58..    "Box  Coil,"  Built  Up  of  Wrought-Iron  Pipe,  for  Indirect- Steam  Heating. 

is  large  as  compared  with  the  exposed  wall  and  window  surface,  we 
should  proceed  as  follows: 

First  compute  the  B.  T.  U.  required  for  loss  by  conduction 
through  walls  and  windows;  and  to  this,  add  the  B.  T.  U.  required 
for  the  necessary  ventilation;  and  divide  the  sum  by  the  efficiency 
of  the  radiators.  An  example  will  make  this  clear. 

Example.  How  many  square  feet  of  indirect  radiation  will  be  required 
to  warm  and  ventilate  a  schoolroom  in  zero  weather,  where  the  heat  loss  by 
conduction  through  walls  and  windows  is  36,000  B.  T.  U.,  and  the  air-supplv 
is  100,000  cubic  feet  per  hour? 

By  the  methods  given  under  "Heat  for  Ventilation,"  we  have 

100,000  X  70  x  127,272  =  B.  T.  U.  required  for  ventilation. 

55 
36,000  +  127,272  -  163,272  B.  T.  U.  =  Total  heat  required. 

This  in  turn  divided  by  600  (the  efficiency  of  indirect  radiators 
under  these  conditions)  gives  272  square  feet  of  surface  required. 


271 


76  HEATING  AND  VENTILATION 

In  the  case  of  a  dwelling-house  the  conditions  are  somewhat 
changed,  for  a  room  having  a  comparatively  large  exposure  will  have 
perhaps  only  2  or  3  occupants,  so  that,  if  the  small  air-quantity  neces- 
sary in  this  case  were  used  to  convey  the  required  amount  of  heat 
to  the  room,  it  would  have  to  be  raised  to  an  excessively  high  temper- 
ature. It  has  been  found  by  experience  that  the  radiating  surface 
necessary  for  indirect  heating  is  about  50  per  cent  greater  than  that 
required  for  direct  heating.  So  for  this  work  we  may  compute  the 
surface  required  for  direct  radiation,  and  multiply  the  result  by  1.5. 

Buildings  like  hospitals  are  in  a  class  between  dwellings  and 
schoolhouses.  The  air-supply  is  based  on  the  number  of  occupants, 
as  in  schools,  but  other  conditions  conform  more  nearly  to  dwelling- 
houses. 

To  obtain  the  radiating  surface  for  buildings  of  this  class,  we 
compute  the  total  heat  required  for  warming  and  ventilation  as  in 
the  case  of  schoolhouses,  and  divide  the  sum  by  the  efficiencies  given 
for  dwellings — that  is,  440  for  zero  weather,  and  460  for  10  degrees 
below. 

Example.  A  hospital  ward  requires  50,000  cubic  feet  of  air  per  hour  for 
ventilation;  and  the  heat  loss  by  conduction  through  walls,  etc.,  is  100,000 
B.  T.  U.  per  hour.  How  many  square  feet  of  indirect  radiation  will  be  required 
to  warm  the  ward  in  zero  weather? 

50,000  X   70   -  55  =  63,630  B.  T.  U.  for   ventilation;   then, 

63,636  +  100,000      „„ 

— —        —  =  3/2  +  square  teet. 

440 

EXAMPLES  FOR   PRACTICE 

1.  A  schoolroom  having  40  pupils  is  to  be  warmed  and  venti- 
lated when  it  is  10  degrees  below  zero.     If  the  heat  loss  by  conduction 
is  30,000  B.  T.  U.  per  hour,  and  the  air  supply  is  to  be  40  cubic  feet 
per  minute  per  pupil,  how  many -square  feet  of  indirect  radiation  will 
be  required?  Axs.  273. 

2.  A  contagious  ward  in  a  hospital  has  10  beds,  requiring  6,000 
cubic  feet  of  air  each,  per  hour.     The  heat  loss  by  conduction  in  zero 
weather  is  80,000  B.  T.  U.     How  many  square  feet  of  indirect  radia- 
tion will  be  required?  Axs.  355. 

3.  The  heat  loss  from  a  sitting  room  is  11,250  B.  T.  U.  per 
hour  in  zero  weather.     How  many  square  feet  of  indirect  radiation 
will  be  required  to  warm  it?  Axs.  75. 


272 


HEATING  AND  VENTILATION 


77 


LAG 
SCREW '£ 


Stacks  and  Casings.  It  has  already  been  stated  that  a  group  of 
sections  connected  together  is  called  a  stack,  and  examples  of  these 
with  their  casings  are  shown  in  Figs.  50  and  51.  The  casings  are 
usually  made  of  galvanized  iron,  and  are  made  up  in  sections  by 
means  of  small  bolts  so  that  they  may  be  taken  apart  in  case  it  is 
necessary  to  make  repairs.  Large  stacks  are  often  enclosed  in  brick- 
work, the  sides  consisting  of  8-inch  walls;  and  the  top  being  covered 
over  with  a  layer  of  brick  and  mortar  supported  on  light  wrought-iron 
tee-bars.  Blocks  of  asbestos  are  sometimes  used  for  covering,  instead 
of  brick,  the  whole  being  covered  over  with  plastic  material  of  the 
same  kind. 

Where  a  single  stack  supplies  several  flues  or  registers,  the 
connections  between  these  and  the  warm-air  chamber  are  made  in 
the  same  manner  as  already  described  for  furnace  heating.  When 
galvanized-iron  casings  are  used,  the  heater  is  supported  by  hangers 
from  the  floor  above.  Fig. 
59  shows  the  method  of 
hanging  a  heater  from  a 
wooden  floor.  If  the  floor 
is  of  fireproof  construc- 
tion, the  hangers  may  pass 
up  through  the  brick- 
work, and  the  ends  be 
provided  with  nuts  and  large  washers  or  plates ;  or  they  may  be  clamped 
to  the  iron  beams  which  carry  the  floor.  WThere  brick  casings  are 
used,  the  heaters  are  supported  upon  pieces  of  pipe  or  light  I-beams 
built  into  the  walls. 

The  warm-air  space  above  the  heater  should  never  be  less  than 
8  inches,  while  12  inches  is  preferable  for  heaters  of  large  size.  The 
cold-air  space  may  be  an  inch  or  two  less;  but  if  there  is  plenty  of 
room,  it  is  good  practice  to  make  it  the  same  as  the  space  above. 

Dampers.  The  general  arrangement  of  a  galvanized-iron  casing 
and  mixing  damper  is  shown  in  Fig.  60.  The  cold-air  duct  is  brought 
along  the  basement  ceiling  from  the  inlet  window,  and  connects 
with  the  cold-air  chamber  beneath  the  heater.  The  entering  air  passes 
up  between  the  sections,  and  rises  through  the  register  above,  as  shown 
by  the  arrows.  When  the  mixing  damper  is  in  its  lowest  position, 
all  air  reaching  the  register  must  pass  through  the  heater;  but  if  the 


IRON 
ffOJD 


nnnnnnnn 


WftO'T   IRON  RIPE 


Fig.  59.    Method  of  Hanging  a  Heater  below  a  Wooden 
Floor. 


S73 


78 


HEATING  AND  VENTILATION 


damper  is  raised  to  the  position  shown,  part  of  the  air  will  pass  by 
without  going  through  the  heater,  and  the  mixture  entering  through 
the  register  will  be  at  a  lower  temperature  than  before.  By  changing 


FLOOR    REG/STEFl 


,,-JJ 


V 

/HEAT, 

r* 

/ 

S 

>                   -- 

J 


GALVANIZED  IRON       SLIDING  DOOR 
CAS/NG 

Fig.  (30.    General  Arrangement  of  a  Galvanizert-Iron  Casing  and  Mixing  Damper. 
Damper  between  Heater  and  Register. 

the  position  of  the  clamper,  the  proportions  of  warm  and  cold  air 
delivered  to  the  room  can  be  varied,  thus  regulating  the  temperatuie 
without  diminishing  to  any  great  extent  the  quantity  of  air  delivered. 


I 


07 


/ 


/ 


COLD  XI  //? 


/ 


^ 


/ 


~y>. 


Fig.  61.    Heater  and  Mixing  Damper  with  Brick  Casing.    Damper  between 
Heater  and  Register. 

The  objection  to  this  form  of  damper  is  that  there  is  a  tendency  for 
the  air  to  enter  the  room  before  it  is  thoroughly  mixed;  that  is,  a 
stream  of  warm  air  will  rise  through  one  half  of  the  register  while 


274 


HEATING  AND  VENTILATION 


7!) 


cold  air  enters  through  the  other.  This  is  especially  true  if  the  con- 
nection between  the  damper  and  register  is  short.  Fig.  61  shows 
a  similar  heater  and  mixing  damper,  with  brick  casing.  Cold  air  is 
admitted  to  the  large  chamber  below  the  heater,  and  rises  through 
the  sections  to  the  register  as  before.  The  action  of  the  mixing 
damper  is  the  same  as  already  described.  Several  flues  or  registers 
may  be  connected  with  a  stack  of  this  form,  each  connection  having, 
in  addition  to  its  mixing  damper,  an  adjusting  damper  for  regulating 
the  flow  of  air  to  the  different  rooms. 

Another  way  of  proportioning  the  air-flow  in  cases  of  this  kind 
is  to  divide  the  hot-air  chamber  above  the  heater  into  sections,  by 
means  of  galvanized-iron  partitions,  giving  to  each  room  its  proper 
share  of  heating  surface.  If  the  cold-air  supply  is  made  sufficiently 
large,  this  arrangement  is  preferable  to  using  adjusting  dampers  as 


i 

- 

1 

I  ft 

^2    -^  --s-r-  -=; 

-»     J~ 

LZj 

^ 

"•»           -^ 

Fig. 


Another  Arrangement  of  Mixing  Damper  and  Heater  in  Galvanized-Iron 
Casing.    Heater  between  Damper  and  Register. 


described  above.  The  partitions  should  be  carried  down  the  full 
depth  of  the  heater  between  the  sections,  to  secure  the  best  results. 
The  arrangement  shown  in  Fig.  62  is  somewhat  different,  and 
overcomes  the  objection  noted  in  connection  with  Fig.  60,  by  sub- 
stituting another.  The  mixing  damper  in  this  case  is  placed  at  the 
other  end  of  the  heater.  When  it  is  in  its  highest  position,  all  of  the 
air  must  pass  through  the  heater  before  reaching  the  register;  but 
when  partially  lowered,  a  part  of  the  air  passes  over  the  heater, 
and  the  result  is  a  mixture  of  cold  and  warm  air,  in  proportions 
depending  upon  the  position  of  the  damper.  As  the  layer  of  warm 
air  in  this  case  is  below  the  cold  air,  it  tends  to  rise  through  it,  and  a 
more  thorough  mixture  is  obtained  than  is  possible  with  the  damper 
shown-in  Fig.  60.  One  quite  serious  objection,  however,  to  this  form 
of  damper,  is  illustrated  in  Fig.  63.  When  the  damper  is  nearly 


875 


HEATING  AND  VENTILATION 


Fig.  63.    Showing  Difficulty  of  Regulat 

iiig  Temperature  with  Arrangement 

in  Fig.  62. 


closed  so  that  the  greater  part  of  the  air  enters  above  the  heater,  it 
has  a  tendency  to  fall  between  the  sections,  as  shown  by  the  arrows, 
and,  becoming  heated,  rises  again,  so  that  it  is  impossible  to  deliver 

air  to  a  room  below  a  certain  tem- 
perature. This  peculiar  action  in- 
creases as  the  quantity  of  air  admit- 
ted below  the  heater  is  diminished. 
When  the  inlet  register  is  placed  in 
the  wall  at  some  distance  above 
the  floor,  as  in  schoolhouse  work,  a  thorough  mixture  of  air  can  be 
obtained  by  plac- 
ing the  heater  so 
that  the  current 
of  warm  air  will 
pass  up  the  front 
of  the  flue  and  be 
discharged  into 
the  room  through 
the  lower  part  of 
the  register.  This 
is  shown  quite 
clearly  in  Fig.  64, 
where  the  cur- 
rent of  warm  air 
is  represented  by 
crooked  arrows, 
and  the  cold  air 
by  straight  ar- 
rows. The  two 
currents  pass  up 
the  flue  separate- 
ly; but  as  soon 
as  they  are  dis- 
charged through  " 

.  ,        Fig.  64.    Arrangement  of  Heater  and  Damper  Causing  Warm  Air 

the    register     the  to  Enter  Room  through  Lower  Part  of  Register,  thus 

°  .  Securing  Thorough  Mixing 

warm   air  tends 

to  rise,  and  the  cold  air  to  fall,  with  the  result  of  a  more  or  less 

complete  mixture,  as  shown. 


H 


O3 


376 


HEATING,  AND  VENTILATION 


It  is  often  desirable  to  warm  a  room  at  times  when  ventilation 
is  not  necessary,  as  in  the  case  of  living  rooms  during  the  night,  or 
for  quick  warming  in  the  morning.  A  register  and  damper  for  air 
rotation  should  be  provided  i  .1  this  case.  Fig.  65  shows  an  arrange- 
ment for  this  purpose.  When  the  damper  is  in  the  position  shown, 
air  will  be  taken  from  the  room  above  and  be  warmed  over  and  over; 
but,  by  raising  the  damper,  the  supply  will  be  taken  from  outside. 
Special  care  should  be  taken  to  make  all  mixing  dampers  tight  against 
air-leakage,  else  their  advantages  will  be  lost.  They  should  work 
easily  and  close  tightly  against  flanges  covered  with  felt.  They  may 
be  operated  from  the  rooms  above  by  means  of  chains  passing  over 


1 

2 

I 

\ 

- 

I 

1 

1 

*OLB  A/fl  DUCT 

^.     : 

•—  v            ) 

—  1  h 

] 

Fig.  i 


Arrangement  for  Quick  Heating  without  Ventilation.    Damper  Shuts  off  Fresh 
Air,  and  Air  of  Room  Heated  by  Rotating  Forth  and  Back  through 
Register  and  Heater. 


guide-pulleys;  special  attachments  should  be 'provided  for  holding 
in  any  desired  position. 

Warm=Air  Flues.  The  required  size  of  the  warm-air  flue  between 
the  heater  and  the  register,  depends  first  upon  the  difference  in  tem- 
perature between  the  air  in  the  flue  and  that  of  the  room,  and  second, 
upon  the  height  of  the  flue.  In  dwelling-houses,  where  the  con- 
ditions are  practically  constant,  it  is  customary  to  allow  2  square 
inches  area  for  each  square  foot  of  radiation  when  the  room  is  on  the 
first  floor,  and  1^  square  inches  for  the  second  and  third  floors.  In 
the  case  of  hospitals,  where  a  greater  volume  of  air  is  required,  these 
figures  may  be  increased  to  3  square  inches  for  the  first  floor  wards, 
and  2  square  inches  for  those  on  the  upper  floors. 

In  schoolhouse  work,  it  is  more  usual  to  calculate  the  size  of 
flue  from  an  assumed  velocity  of  air-flow  through  it.  This  will  vary 
greatly  according  to  the  outside  temperature  and  the  prevailing  wind 
conditions.  The  following  figures  may  be  taken  as  average  velocities 


877 


82  HEATING  AND  VENTILATION 

obtained  in  practice,  and  may  be  used  as  a  basis  for  calculating  the 
required  flue  areas  for  the  different  stories  of  a  school  building: 

1st  floor,  280  feet  per  minute. 
2nd     "  ,  340     " 
3rd      "  ,  400     " 

These  velocities  will  be  increased  somewhat  in  cold  and  windy  weather 
arid  will  be  reduced  when  the  atmosphere  is  mild  and  damp. 

Having  assumed  these  velocities,  and  knowing  the  number  of 
cubic  feet  of  air  to  be  delivered  to  the  room  per  minute,  we  have  only 
to  divide  this  quanity  by  the  assumed  velocity,  to  obtain  the  required 
'flue  area  in  square  feet. 

Example.  A  schoolroom  on  the  second  floor  is  to  have  an  air-supply  of 
2,000  cubic  feet  per  minute.  What  will  be  the  required  flue  area? 

Axs.     2000  -T-  340  =  5.8  +  sq.  feet. 

The  velocities  would  be  higher  in  the  coldest  weather,  and  dampers 
should  be  placed  in  the  flues  for  throttling  the  air-supply  when  nec- 
essary. 

Cold=Air  Ducts.  The  cold-air  ducts  supplying  heaters  should 
be  planned  in  a  manner  similar  to  that  described  for  furnace  heating. 
The  air-inlet  should  be  on  the  north  or  west  side  of  the  building;  but 
this  of  course  is  not  always  possible.  The  method  of  having  a  large 
trunk  line  or  duct  with  inlets  on  fwo  or  more  sides  of  the  building, 
should  be  carried  out  when  possible.  A  cold-air  room  with  large 
inlet  windows,  and  ducts  connecting  with  the  heaters,  makes  a  good 
arrangement  for  schoolhouse  work.  The  inlet  windows  in  this  case 
should  be  provided  with  check-valves  to  prevent  any  outward  flow  of 
air.  A  detail  of  this  arrangement  is  shown  in  Fig.  66. 

This  consists  of  a  boxing  around  the  window,  extending  from 
the  floor  to  the  ceiling.  The  front  is  sloped  as  shown,  and  is  closed 
from  the  ceiling  to  a  point  below  the  bottom  of  the  window.  The 
remainder  is  open,  and  covered  with  a  wire  netting  of  about  ^-inch 
mesh;  to  this  are  fastened  flaps  or  checks  of  gossamer  cloth  about 
6  inches  in  width.  These  are  hemmed  on  both  edges  and  a  stout 
wire  is  run  through  the  upper  hem  which  is  fastened  to  the  netting 
by  means  of  small  copper  or  soft  iron  wire.  The  checks  allow  the  air 
to  flow  inward  but  close  when  there  is  any  tendency  for  the  current 
to  reverse. 

The  area  of  the  cold-air  duct  for  any  heater  should  be  about 
three-fourths  the  total  area  of  the  warm-air  ducts  leading  from  it. 


278 


HEATING  AND  VENTILATION 


83 


If  the  duct  is  of  any  considerable  length  or  contains  sharp  bends,  it 
should  be  made,  the  full  size  of  all  the  warm-air  ducts.  Adjusting 
dampers  should  be  placed  in  the  supply  duct  to  each  separate  stack. 
If  a  trunk  with  two  inlets  is  used,  each  inlet  should  be  of  sufficient 
size  to  furnish  the  full  amount  of  air  required,  and  should  be  pro- 
vided with  cloth  checks  for  preventing  an  outward  flow  of  air,  as 
already  described.  The  inlet  windows  should  be  provided  with 
some  form  of  damper  or  slide,  outside  of  which  should  be  placed  a 
wire  grating,  backed  by  a  netting  of  about  f-inch  mesh. 

Vent  Flues.  In  dwelling-houses,  vent  flues  are  often  omitted, 
and  the  frequent  opening  of  doors  and  leakage  are  depended  upon  to 
carry  away  the  im- 
pure air.  A  well- 
designed  system  of 
warming  should 
provide  some  means 
for  discharge  ven- 
tilation, especially 
for  bathrooms  and 
toilet-rooms,  and 
also  for  living  rooms 
where  lights  are 
burned  in  the  even- 
ing. Fireplaces  are 
usually  provided  in 
the  more  important 
rooms  of  a  well- 
built  house,  and 
these  are  made  to 

serve  as  vent  flues.  In  rooms  having  no  fireplaces,  special  flues 
of  tin  or  galvanized  iron  may  be  carried  up  in  the  partitions  in 
the  same  manner  as  the  warm-air  flues.  These  should  be  gathered 
together  in  the  attic,  and  connected  with  a  brick  flue  running  up 
beside  the  boiler  or  range  chimney. 

Very  fair  results  may  be  obtained  by  simply  letting  the  flues  open 
into  an  unfinished  attic,  and  depending  upon  leakage  through  the 
roof  to  carry  away  the  foul  air. 


Fig.  66.    Air-Inlet  Provided  with  Check-Valves  to  Prevent 
Outward  Flow  of  Air. 


979 


HEATING  AND  VENTILATION 


The  sizes  of  flues  may  be  made  the  reverse  of  the  warm-air  flues 
— that  is,  1-2-  square  inches  area  per  square  foot  of  indirect  radiation 
for  rooms  on  the  first  floor,  and  2  square  inches  for  those  on  the 
second.  This  is  because  the  velocity  of  flow  will  depend  upon  the 
height  of  flue,  and  will  therefore  be  greater  from  the  first  floor.  The 
flow  of  air  through  the  vents  will  be  slow  at  best,  unless  some  means 
is  provided  for  warming  the  air  in  the  flue  to  a  temperature  above 
that  of  the  room  with  which  it  connects. 

The  method  of  carrying  up  the  outboard  discharge  beside  a  warm 
chimney  is  usually  sufficient  in  dwelling-houses;  but  when  it  is 

desired  to  move  larger 
quantities  of  air,  a  loop 
of  steam  pipe  should  be 
run  inside  the  flue.  This 
should  be  connected  for 
drainage  and  air-venting 
as  shown  in  Fig.  67. 
When  vents  are  carried 
through  the  roof  inde- 
pendently, some  form  of 
protecting  hood  should 
be  provided  for  keeping 
out  the  snowr  and  rain. 
A  simple  form  is  shown 
in  Fig.  68.  Flues  carried 
outboard  in  this  way 
should  always  be  ex- 


Air 
Valvt 


Ste<am 


Return 


Fig.  67.    Loop  of  Steam  Pip:*  to  be  Run  Inside  Flue 
Connected  for  Drainage  and  Air- Venting. 


tended  well  above  the  ridges  of  adjacent  roofs  to  prevent  down 
drafts  in  windy  weather. 

For  schoolhouse  work  we  may  assume  average  velocities  through 
the  vent  flues,  as  follows: 

1st  floor,  340  feet  per  minute. 
2nd     "  ,  280    "      " 
3rd      "  ,  220    "      " 

Where  flue  sizes  are  based  on  these  velocities,  it  is  well  to  guard 
against  down  drafts  by  placing  an  aspirating  coil  in  the  flue.  A 
single  row  of  pipes  across  the  flue  as  shown  in  Fig.  69,  is  usually 
sufficient  for  this  purpose  when  the  flues  are  large  and  straight; 


280 


HEATING  AND  VENTILATION 


otherwise,  two  rows  should  be  provided.  The  slant  height  of  the 
heater  should  be  about  twice  the  depth  of  the  flue,  so  that  the  area 
between  the  pipes  shall  equal  the 
free  area  of  the  flue. 

Large  vent  flues  of  this  kind 
should  always  be  provided  with 
dampers  for  closing  at  night,  and 
for  regulation  during  strong  winds. 

Sometimes  it  is  desired  to  move 
a  given  quantity  of  air  through  a 
flue  which  is  already  in  place. 
Table  XXIV  shows  what  velocities 
may  be  obtained  through  flues  of 
different  heights,  for  varying  dif- 
ferences in  temperature  between  the 
outside  air  and  that  in  the  flue. 

.  Example. — It  is  desired  to  discharge  1,300  cubic  feet  of  air  per  minute 
through  a  flue  having  an  area  of  4  square  feet  and  a  height  of  30  feet.  If  the 
efficiency  of  an  aspirating  coil  is  400  B.  T.  U.,  how  many  square  feet  of  surface 
will  be  required  to  move  this  amount  of  air  when  the  temperature  of  the  room 
is  70°  and  the  outside  temperature  is  60°? 


/^/povr 
Hfl 


Fig.  68.    Section  Showing  Simple  Form 
of  Protecting  Hood  for  Vent  Car- 
ried through  Roof. 


Fig.  69.    Aspirating  Coil  Placed  in  Flue  to  Prevent  Down  Drafts. 

1,300  -T-  4  =  325  feet  per  minute  =  Velocity  through  the  flue. 
Looking  in  Table  XXIV,  and  following  along  the  line  opposite  a 
30-foot  flue,  we  find  that  to  obtain  this  velocity  there  must  be  a  differ- 
ence of  30  degrees  between  the  air  in  the  flue  and  the  external  air. 


281 


HEATING  AND  VENTILATION 


If  the  outside  temperature  is  60  degrees,  then  the  air  in  the  flue  must 
he  raised  to  60  +  30  =  90  degrees.  The  air  of  the  room  being  at 
70  degrees,  a  rise  of  20  degrees  is  necessary.  So  the  problem  resolves 
itself  into  the  following:  What  amount  of  heating  surface  having  an 

TABLE  XXIV 

Air=Flow  through  Flues  of  Various  Heights  under  Varying 
Conditions  of  Temperature 

(Volumes  given  in  cubic  feet  per  square  foot  of  sectional  area  of  flue) 


HEIGHT  OF 
FLUE 
IN  FEKT 

5^ 

10°         15° 

20°         30  =• 

50* 

5 

55 

76 

94 

109 

134 

167 

10 

77 

108 

133 

153 

188 

242 

15 

94 

133 

162 

188 

230 

297 

20 

108 

153 

188 

217 

265 

342 

25 

121 

171 

210 

242 

297 

383 

30 

133 

188 

230 

265 

325 

419 

35 

143 

203 

248       286 

351 

453 

40 

1  53 

217 

265       306 

375 

484 

45 

162 

230 

282 

325 

39.8 

514 

50 

.   171 

242 

297       342 

419 

541 

GO 

188 

264       325 

373 

461 

594 

efficiency  of  400  B.  T.  U.  is  necessary  to  raise  1,300  cubic  feet  of  air 
per  minute  through  20  degrees? 

1,300  cubic  feet  per  minute  =  1,300  X  60  =  7S,()()()  per  hour; 
and  making  use  of  our  formula  for  "heat  for  ventilation,"  we  have 
78.000  X  20  =  28j3(.3BTU. 

55 
and  this  divided  by  400  =  71  square  feet  of  heating  surface  required. 

EXAMPLES    FOR    PRACTICE 

1.  A  schoolroom  on  the  third  floor  has   50   pupils,  who   are 
to  be  furnished  with  30  cubic  feet  of  air  per  minute  each.     What  will 
be  the  required  areas  in  square  feet  of  the  supply  and  vent  flues? 

Axs.  Supply,  3.7  +.     Vent,  6.8  +. 

2.  What  size  of  heater  will  be  required  in  a  vent  flue  40  feet 
high  and  with  an  area  of  5  square  feet,  to  enable  it  to  discharge  1,530 
cubic  feet  per  minute,  when  the  outside  temperature  is  60°?     (Assume 
an  efficiency  of  400  B.  T.  U.  for  the  heater.)     Axs.  41 .7  square  feet. 


HEATING  AND  VENTILATION 


87 


Registers.    Registers  are  made  of  cast  iron  and  bronze,  in  a 
great  variety  of  sizes  and  patterns.     The  almost  universal  finish  for 
cast-iron  registers  is  black  "Japan;"  but  they  are  also  finished  in 
colors  and  electroplated  with 
copper   and    nickel.     Fig.    70 
shows    a    section    through    a 
floor  register,  in  which  A  rep- 
resents the  valves,  which  may 
be  turned  in  a  vertical  or  hori- 
zontal position,  thus  opening 


Fig.  70.    Section  through  a  Floor  Register. 


or  closing  the  register;  B  is  the 
iron  border;  C,  the  register  box 
of  tin  or  galvanized  iron;  and  D,  the  warm-air  pipe.  Floor  registers 
are  usually  set  in  cast-iron  borders,  one  of  which  is  shown  in  Fig.  71 ; 
while  wall  registers  may  be  screwed  directly  to  wooden  borders  or 
frames  to  correspond  with  the  finish  of  the  room.  Wall  registers 
should  be  provided  with  pull-cords  for  opening  and  closing  from  the 
floor;  these  are  shown  in  Fig.  72.  The  plain  lattice  pattern  shown  in 
Fig.  73  is  the  best  for  schoolhouse  work,  as  it  has  a  comparatively 

free  opening  for 
air-flow  and  is 
pleasing  and  sim- 
ple in  design. 
More  elaborate 
patterns  are  used 
for  fine  dwelling- 
house  work. 
Registers  with 
shut-off  valves 
are  used  for  air- 
inlets,  while  the 
plain  register 
faces  without  the 
valves  are  placed 
in  the  vent  open- 
ings. The  vent  flues  are  usually  gathered  together  in  the  attic,  and 
a  single  damper  may  be  used  to  shut  off  the  whole  number  at  once. 
Flat  or  round  wire  gratings  of  open  pattern  are  often  used  in  place  of 


Cast-Iron  Border  for  a  Floor  Register. 


HEATING  AND  VENTILATION 


register  faces.  The  grill  or  solid  part  of  a  register  face  usually  takes 
up  about  £  of  the  area;  hence  in  computing  the  size,  we  must  allow 
for  this  by  multiplying  the  required  "net  area"  by  1 .5,  to  obtain  the 
"total"  or  "over-all"  area. 

Example.  Suppose  we  have  a  flue  10  inc-hes  in  width  and  wish  to  use  a 
register  bavins:  a  free  area  of  200  square  inches.  What  will  he  the  required 
height  of  the  register? 

200  X  1.5  =  300  square  inches,  which  is  the  total  area  required; 
then  300  -r-  10  =  30,  which  is  the  required  height,  and  we  should  use 
a  10  by  30-inch  register.  When  a  register  is  spoken  of  as  a  10  by 


ir 


IB 


IVENTILATORJ 
FOR 

CORDS 


_ 


j 


Fig.  72.     Wall  Register  with  Pull 

Cords  for  Opening  and 

Closing. 


Fig.  73.    Plain  Lattice  Pattern  Register.    Best 
for  Schoolhouse  Work. 


30-inch  or  a  10  by  20-inch,  etc.,  the  dimensions  of  the  latticed  opening 
are  meant,  and  not  the  outside  dimensions  of  the  whole  register.  The 
free  opening  should  have  the  same  area  as  the  flue  with  which  it  con- 
nects. In  designing  new  work,  one  should  provide  himself  with  a 
trade  catalogue,  and  use  only  standard  sizes,  as  special  patterns  and 
sizes  are  costly.  Fig.  74  shows  the  method  of  placing  gossamer 
check-valves  back  of  the  vent  register  faces  to  prevent  down  drafts, 
the  same  as  described  for  fresh-air  inlets. 


HEATING  AND  VENTILATION 


Inlet  registers  in  dwelling-house  and  similar  work  are  placed 
either  in  the  floor  or  in  the  baseboard ;  sometimes  they  are  located 
under  the  windows,  just  above  the  baseboard.  The  object  in  view 
is  to  place  them  where  the  currents  of  air  entering  the  room  will  not 
be  objectionable  to  persons  sitting  near  windows.  A  long,  narrow 
floor-register  placed  close  to  the  wall  in  front  of  a  window,  sends 
up  a  shallow  current  of  warm  air,  which  is  not  especially  noticeable 


COSSAMER 
CHECKS 


WIRE 
NETTING 


•   Wig.  74.    Method  of  Placing  Gossamer  Check- Valves  back  of  Vent  Register  Face 
to  Prevent  Down  Drafts. 

to  one  sitting  near  it.  Inlet  registers  are  preferably  placed  near 
outside  walls,  especially  in  large  rooms.  Vent  registers  should  be 
placed  in  inside  walls,  near  the  floor. 

Pipe  Connections.  The  two-pipe  system  with  dry  or  sealed 
returns  is  used  in  indirect  heating.  The  conditions  to  be  met  are 
practically  the  same  as  in  direct  heating,  the  only  difference  being 
that  the  radiators  are  at  the  basement  ceiling  instead  of  on  the  floors 
above.  The  exact  method  of  making  the  pipe  connections  will 
depend  somewhat  upon  existing  conditions;  but  the  general  method 
shown  in  Fig.  75  may  be  used  as  a  guide,  with  modifications  to  suit 


90 


HEATING  AND  VENTILATION' 


any  special  case.     The  ends  of  all  supply  mains  should  be  dripped, 
and  the  horizontal  returns  should  be  sealed  if  possible. 

Pipe  Sizes.  The  tables  already  given  for  the  proportioning  of 
pipe  sizes  can  be  used  for  indirect  systems.  The  following  table  has 
been  computed  for  an  efficiency  of  640  B.  T.  U.  per  square  foot  of 
surface  per  hour,  which  corresponds  to  a  condensation  of  -,  of  a  pound 
of  steam.  This  is  twice  that  allowed  for  direct  radiation  in  Table 


DRfP 


WATER          L/Aff 


MAIN     RETURN 


Fig. 


iort  of  Makintr  Pipe  and  Radiator  Connections,  in  Basement, 
in  In  lireet  Heating. 


XVII;  so  that  we  can  consider  1  square  foot  of  indirect  surface  as 
equal  to  2  of  direct  in  computing  pipe  sizes. 

As  the  indirect  heaters  are  placed  in  the  basement,  care  must  b.e 
taken  that  the  bottom  of  the  radiator  does  not  come  too  near  the 
water-line  of  the  boiler,  or  the  condensation  will  not  flow  back  prop- 
erly; this  distance,  under  ordinary  conditions,  should  not  be  less  than 
2  feet.  If  much  less  than  this,  the  pipes  should  be  made  extra  large, 
so  that  there  may  be  little  or  no  drop  in  pressure  between  the  boiler 


HEATING  AND  VENTILATION 


'.U 


TABLE    XXV 
Indirect  Radiating  Surface  Supplied  by  Pipes  of  Various  Sizes 


SQUARE  FEET  OF  INDIRECT  RADIATION  WHICH  WILL  BE  SUPPLIED  WITH 

SIZK  OF  PIPE 

1  Pound  Drop  in  200  Feet 

1  Pound  Drop  in  1  00  Feet 

i  Pound  Drop  in  100  Feet 

1   in. 

28    • 

40 

57 

51 

72 

105 

H 

67 

95 

170 

2 

185 

262 

375 

2* 

335 

475 

675 

3 

540 

775 

1,  105 

3| 

812 

1,  160 

1,645 

4 

1,  140 

1,625 

2,310 

5 

2,030 

2,900 

4,  110 

6 

3,  260 

4,  660 

6,  600 

7 

4,830 

.6,  900 

9,810 

8 

6,800 

9,720 

13,860 

and  the  heater.     A  drop  in  pressure  of  1   pound   would  raise  the 
water-lme  at  the  heater  2.4  feet. 


— -_ 


Fig.  76.    General  Form  of  Direct-Indirect       Fig. 
Radiator. 


Radiator  Shown 


Direct=Indirect  Radiators.     A  direct-indirect  radiator  is  similar 
in  form  to  a  directx  radiator,  and  is  placed  in  a  room  in  the  same 


287 


92  HEATING  AND  VENTILATION 

manner.  Fig.  76  shows  the  general  form  of  this  type  of  radiator; 
and  Fig.  77  shows  a  section  through  the  same.  The  shape  of  the 
sections  is  such,  that  when  in  place,  small  flues  are  formed  between 
them.  Air  is  admitted  through  an  opening  in  the  outside  wall;  and, 
in  passing  upward  through  these  flues,  becomes  heated  before  enter- 
ing the  room.  A  switch-damper  is  placed  in  the  duct  at  the  base  of 
the  radiator,  so  that  the  air  may  be  taken  from  the  room  itself  instead 
•  1  from  out  of  doors,  if  so  desired.  This  is  shown  more  particularly 
in  Fig.  7(>. 

Fig.  78  shows  the  wall  box  provided  with  louvre  slats  and  netting, 
through  which  the  air  is  drawn.  A  damper  door  is  placed  at  either 

end  of  the  radiator  base; 
and,  if  desired,  when  the 
cold-air  supply  is  shut  off 
by  means  of  the  register 
in  the  air-duct,  the  radia- 
tor can  be  converted  into 
the  ordinary  type  by 
opening  both  damp'er 
doors,  thus  taking  the  air 

?  ,1  , 

irom  the  room  instead 
of  from  the  outside.  It  is  customary  to  increase  the  size  of  a  direct- 
indirect  radiator  30  per  cent  above  that  called  for  in  the  case  of 
direct  heating. 

CARE  AND  MANAGEMENT  OF  STEAM= 
HEATING  BOILERS 

Special  directions  are  usually  supplied  by  the  maker  for  each 
kind  of  boiler,  or  for  those  which  are  to  be  managed  in  any  peculiar 
way.  The  following  general  directions  apply  to  all  makes,  and  may 
be  used  regardless  of  the  type  of  boiler  employed: 

Before  starting  the  fire,  see  that  the  boiler  contains  sufficient 
water.  The  water-line  should  be  at  about  the  center  of  the  gauge- 
glass. 

The  smoke-pipe  and  chimney  flue  should  be  clean,  and  the  draft 
good. 

Build  the  fire  in  the  usual  way,  using  a  quality  of  coal  which  is 
best  adapted  to  the  heater.  In  operating  the  fire,  keep  the  firepot 


HEATING  AND  VENTILATION  93 

full  of  coal,  and  shake  down  and  remove  all  ashes  and  cinders  as  often 
as  the  state  of  the  fire  requires  it. 

Hot  ashes  or  cinders  must  not  be  allowed  to  remain  in  the  ashpit 
under  the  grate-bars,  but  must  be  removed  at  regular  intervals  to 
prevent  burning  out  the  grate. 

To  control  the  fire,  see  that  the  damper  regulator  is  properly 
attached  to  the  draft  doors  and  the  damper;  then  regulate  the  draft 
by  weighting  the  automatic  lever  as  may  be  required  to  obtain  the 
necessary  steam  pressure  for  warming.  Should  the  water  in  the 
boiler  escape  by  means  of  a  broken  gauge-glass,  or  from  any  other 
cause,  the  fire  should  be  dumped,  and  the  boiler  allowed  to  cool  before 
adding  cold  water. 

An  empty  boiler  should  never  be  filled  when  hot.  If  the  water 
gets  low  at  any  time,  but  still  shows  in  the  gauge-glass,  more  water 
should  be  added  by  the  means  provided  for  this  purpose. 

The  safety-valve  should  be  lifted  occasionally  to  see  that  it  is 
in  working  order. 

If  the  boiler  is  used  in  connection  with  a  gravity  system,  it  should 
be  cleaned  each  year  by  filling  with  pure  water  and  emptying  through 
the  blow -off.  If  it  should  become  foul  or  dirty,  it  can  be  thoroughly 
cleansed  by  adding  a  few  pounds  of  caustic  soda,  and  allowing  it  to 
stand  for  a  day,  and  then  emptying  and  thoroughly  rinsing. 

During  the  summer  months,  it  is  recommended  that  the  water 
be  drawn  off  from  the  system,  and  that  air-valves  and  safety-valves 
be  opened  to  permit  the  heater  to  dry  out  and  to  remain  so.  Good 
results,  however,  are  obtained  by  filling  the  heater  full  of  water, 
driving  off  the  air  by  boiling  slowly,  and  allowing  it  to  remain  in  this 
condition  until  needed  in  the  fall.  The  water  should  then  be  drawn 
off  and  fresh  water  added. 

The  heating  surface  of  the  boiler  should  be  kept  clean  and  free  from 
ashes  and  soot  by  means  of  a  brush  made  especially  for  this  purpose. 

Should  any  of  the  rooms  fail  to  heat,  examine  the  steam  valves 
in  the  radiators.  If  a  two-pipe  system,  both  valves  at  each  radiator 
must  be  opened  or  closed  at  the  same  time,  as  required.  See  that 
the  air-valves  are  in  working  condition. 

If  the  building  is  to  be  unoccupied  in  cold  weather,  draw  all  the 
water  out  of  the  system  by  opening  the  blow-off  pipe  at  the  boiler  and 
all  steam  valves  and  air-valves  at  the  radiators. 


HEATING  AND  VENTILATION 


HOT= WATER    HEATERS 

Types.  Hot-water  heaters  differ  from  steam  boilers  principally 
in  the  omission  of  the  reservoir  or  space  for  steam  above  the  heating 
surface.  The  steam  boiler  might  answer  as  a  heater  for  hot  water; 

but  the  large  capacity 
left  for  the  steam  would 
tend  to  make  its  opera- 
tion slow  and  rather 
unsatisfactory,  although 
the  same  type  of  boiler 
is  sometimes  used  for 
both  steam  and  hot 
water.  The  passages  in 
a  hot-water  heater  need 
not  extend  so  directly 
from  bottom  to  top  as 
in  a  steam  boiler,  since 
the  problem  of  provid- 
ing for  the  free  liberation 
of  the  steam  bubbles 
does  not  have  to  be  con- 
sidered. In  general,  the 
heat  from  the  furnace 
should  strike  the  sur- 
faces in  such  a  manner 
as  to  increase  the  natural 
circulation;  this  may  be 
accomplished  to  a  cer- 
tain extent  by  arranging 
the  heating  surface  so 
that  a  large  proportion 
of  the  direct  heat  will 
be  absorbed  near  the 
top  o  f -  t'h  e  heater. 

Practically  the  boilers  for  low-pressure  steam  and  for  hot  water  differ 
from  each  other  very  little  as  to  the  character  of  the  heating  surface, 
so  that  the  methods  already  given  for  computing  the  size  of  grate 
surface,  horse-power,  etc.,  under  the  head  of  "Steam  Boilers,"  can  be 


Richardson  Sectional  Hot-Water  Heater. 


HEATING  AND  VENTILATION 


95 


used    with   satisfactory   results   in   the   case   of   hot-water  heaters. 

It  is  sometimes  stated  that,  owing  to  the  greater  difference  in  tem- 
perature between  the  furnace  gases  and  the  .water  in  a  hot-water 
heater,  as  compared  with  steam,  the  heating  surface  will  be  more 
efficient  and  a  smaller  heater  can  be  used.  While  this  is  true  to  a 
certain  extent,  different  authorities  agree  that  this  advantage  is  so 
small  that  no  account  should  betaken  of  it,  and  the  general  propor- 
tions of  the  heater  should  be  calculated  in  the  same  manner  as  for 
steam.  Fig.  79  shows  a  form  of  hot-water  heater  made  up  of  slabs 
or  sections  similar  to  the  sectional  steam  boiler  shown  in  Part  I. 
The  size  can  be  increased  in  a  similar  manner,  by  adding  more 
sections.  In  this  case,  however,  the  boiler  is  increased  in  width  in- 
stead of  in  length.  This  has  an  advantage  in  the  larger  sizes,  as  a 
second  fire  door  can 
be  added,  and  all 
parts  of  the  grate 
can  be  reached  as 
well  in  the  large  sizes 
as  in  the  small. 

Fig.  80  shows  a 
different  form  of  sec- 
tional boiler,  in  which 
the  sections  are 
placed  one  above  an- 
other. These  boilers 
are  circular  in  form 
and  well  adapted  to 
dwelling-houses  and 
similar  work. 

Fig.  81  shows  another  type  of  cast-iron  heater  which  is  not  made 
in  sections.  The  space  between  the  outer  and  inner  shells  surround- 
ing the  furnace  is  filled  with  water,  and  also  the  cross-pipes  directly 
over  the  fire  and  the  drum  at  the  top.  The  supply  to  the  radiators 
is  taken  off  from  the  top  of  the  heater,  and  the  return  connects  at  the 
lowest  point. 

The  ordinary  horizontal  and  vertical  tubular  boilers,  with  various 
modifications,  are  used  to  a  considerable  extent  for  hot-water  heating, 


Fig.  80, 


Invincible"  Boiler,  with  Sections 

Superposed. 
Courtesy  of  American  Radiator  Co. 


291 


96 


HEATING  AXD  VENTILATION 


and  are  well  adapted  to  this  class  of  work,  especially  in  the  case  of 
large  buildings. 

Automatic  regulators  are  often  used  for  the  purpose  of  main- 
taining a  constant  temperature  of  the  water.  They  are  constructed 
in  different  ways — some  depend  upon  the  expansion  of  a  metal  pipe 
or  rod  at  different  temperatures,  and  others  upon  the  vaporization 

and  consequent  pres- 
sure of  certain  volatile 
liquids.  These  means 
are  usually  employed 
to  open  small  valves 
which  admit  water- 
pressure  under  rubber 
diaphragms;  and  these 
in  turn  are  connected 
by  means  of  chains 
with  the  draft  doors 
of  the  furnace,  and  so 
regulate  the  draft  as 
required  to  maintain 
an  even  temperature 
of  the  water  in  the 
heater.  Fig.  82  shows 
one  of  the  first  kind. 
.1  is  a  metal  rod  placed 
in  the  flow  pipe  from 
the  heater,  and  is  so 
connected  with  the 
valve  B  that  when  the 
water  reaches  a  certain 

temperature  the  expansion  of  the  rod  opens  the  valve  and  admits 
water  from  the  street  pressure  through  the  pipes  C  and  D  into  the 
chamber  E.  The  bottom  of  E  consists  of  a  rubber  diaphragm, 
which  is  forced  down  by  the  water-pressure  and  carries  with  it  the 
1-ever  which  operates  the  dampers  as  shown,  and  checks  the  fire. 
When  the  temperature  of  the  water  drops,  the  rod  contracts  and 
valve  B  closes,  shutting  off  the  pressure  from  the  chamber  E.  A 
spring  is  provided  to  throw  the  lever  back  to  ita  original  position, 


Fig.  81      Cast-Iron  Heater  Not  Made  in  Sections.     Water 
Fills  Cross-Pipes  and  Space  between  Outer  and 


es  and  Space  be 
Inner  Shells. 


293 


HEATING  AN£>  VENTILATION 


'.17 


and  the  water  above  the  diaphragm  is  forced  out  through  the  pet- 
cock  G,  which  is  kept  slightly  open  all  the  time. 

DIRECT  HOT=WATER  HEATING 

A  hot-water  system  is  similar  in  construction  and  operation  to 
one  designed  for  steam,  except  that  hot  water  flows  through  the 
pipes  and  radiators  instead. 

The  circulation  through  the  pipes  is  produced  solely  by  the  dif- 
ference in  weight  of  the 
water  in  the  supply  and 
return,  due  to  the  differ- 
e n c e  in  temperature.. 
When  water  is  heated  it 
expands,  and  thus  a 
given  volume  becomes 
lighter  and  tends  to  rise, 
and  the  cooler  water  flows 
in  to  take  its  place;  if  the 
application  of  heat  is  kept 
up,  the  circulation  thus 
produced  is  continuous. 
The  velocity  of  flow  de- 
pends upon  the  difference 
in  temperature  between 
the  supply  and  return, 
and  the  height  of  the 
radiator  above  the  boiler. 
The  horizontal  distance 
of  the  radiator  from  the 
boiler  is  also  an  important  factor  affecting  the  velocity  of  flow. 

This  action  is  best  shown  by  means  of  a  diagram,  as  in  Fig.  83. 
If  a  glass  tube  of  the  form  shown  in  the  figure  is  filled  with  water  and 
held  in  a  vertical  position,  no  movement  of  the  water  will  be  noticed, 
because  the  two  columns  A  and  B  are  of  the  same  weight,  and  there- 
fore in  equilibrium.  Now,  if  a  lamp  flame  be  held  near  the  tube  A, 
the  small  bubbles  of  steam  which  are  formed  will  show  the  water 
to  be  in  motion,  with  a  current  flowing  in  the  direction  indicated  by 
the  arrows.  The  reason  for  this  is,  that,  as  the  water  in  A  is  heated, 


Fig.  82.    Hot- Water  Heater  with  Automatic  Regu- 
lator Operated  through  Expansion  and  Con- 
traction of  Metal  Rod  in  Flow  Pipe. 


IIKATIXG  AND  VENTILATION 


Fig.  S3.  Illustrating 
How  the  Heating 
of  Water  Causes 
Circulation. 


it  expands  and  becomes  lighter  for  a  given  volume,  and  is  forced 

upward  by  the  heavier  water  in  B  falling  to  the  bottom  of  the  tube. 

The  heated  water  flows  from  .1  through  the  connecting  tube  at  the 
top,  into  B,  where  it  takes  the  plaee  of  the 
cooler  water  which  is  settling  to  the  bottom.  If, 
now,  the  lamp  be  replaced  by  a  furnace,  and  the 
columns  A  and  B  be  connected  at  the  top  by 
inserting  a  radiator,  the  illustration  will  assume 
the  practical  form  as  utilized  in  hot-water  heating 
(see  Fig.  84). 

The  heat  given  off  by  the  radiator  always 
insures  a  difference  in  temperature  between  the 
columns  of  water  in  the  supply  and  return  pipes, 
so  fliat  as  long  as  heat  is  supplied  by  the  furnace 
the  flow  of  water  will  continue.  The  greater  the 

difference  in  temperature  of  the  water  in  the  two  pipes,  the  greater 

the  difference  in  weight,   and  con- 
sequently the  faster  the  flow.     The 

greater  the  height   of   the   radiator 

above  the  heater,  the    more    rapid 

will  be  the  circulation,  because  the 

total   difference    in   weight  between 

the  water  in  the  supply  and   return 

risers   will    vary  directly  with  their 

height.    From  the  above  it  is  evident 

that   the   rapidity  of   flow   depends 

chiefly  upon  the  temperature  differ- 
ence between  the  supply  and  return, 

and  upon  the  height  of  the  radiator 

above   the  heater.     Another   factor 

which   must   be  considered  in  long 

runs  of  horizontal  pipe  is  the  fric- 

iional  resistance. 

Systems  of  Circulation.     There 

are     two     distinct    systems    of    cir- 
culation employed — one  depending 

on    the    difference    in    temperature 

of  the  water  in  the  supply  and  return  pipes,  called  gravity  circulation; 


D- 


Fig.  84.    Illustrating  Simple  Circula- 
tion in  a  Heating  System. 


294 


HEATING  AND  VENTILATION 


i 


f 


and  another  where  a  pump  is  used  to  force  the  water  through  the 
mains,  called  forced  circulation.  The  former  is  used  for  dwellings 
and  other  buildings  of  ordinary  size,  and  the  latter  for  large  buildings, 
and  especially  where  there  are  long  horizontal  runs  of  pipe. 

For  gravity  circulation  some  form  of  sectional  cast-iron  boiler 
is  commonly  used,  although  wrought-iron  tubular  boilers  may  be 
employed  if  desired.  In  the  case  of  forced  circulation,  a  heater  de- 
signed to  warm  the  water  by  means  of  live  or  exhaust  steam  is  often 
used.  A  centrifugal  or  rotary  pump  is  best  adapted  to  this  pur- 
pose, and  may  be  driven  by  an  electric  motor  or  a  steam  engine, 
as  most  convenient. 

Types  of  Radiating  Surface.     Cast-iron  radiators  and  circulation 

coils  are  used  for  hot  water  as       _^ }  — ^ 

well  as  for  steam.  Hot-water  *~| 
radiators  differ  from  steam 
radiators  principally  in  having 
a  horizontal  passage  at  the  top 
as  well  as  at  the  bottom. 
This  construction  is  necessary 
in  order  to  draw  off  the  air 
which  gathers  at  the  top  of 
each  loop  or  section.  Other- 
wise they  are  the  same  as 
steam  radiators,  and  are  well 
adapted  for  the  circulation  of  F^c 
steam,  and  in  some  respects 
are  superior  to  the  ordinary  pattern  of  steam  radiator. 

The  form  shown  in  Fig.  85  is  made  with  an  opening  at  the  top 
for  the  entrance  of  water,  and  at  the  bottom  for  its  discharge,  thus 
insuring  a  supply  of  hot  water  at  the  top  and  of  colder  water  at  the 
bottom. 

Some  hot-water  radiators  are  made  with  a  cross-partition  so 
arranged  that  all  water  entering  passes  at  once  to  the  top,  from  which 
it  may  take  any  passage  toward  the  outlet.  Fig.  86  is  the  more 
common  form  of  radiator,  and  is  made  with  continuous  passages  at 
top  and  bottom,  the  hot  water  being  supplied  at  one  side  and  drawn 
off  at  the  other.  The  action  of  gravity  is  depended  upon  for  making 
the  hot  and  lighter  water  pass  to  the  top,  and  the  colder  water  sink 


:  Showing  Construction  of  Radiator  for 

ot  Water  or  Steam.    Note  Horizontal  Pas- 
sage along  Top. 


100 


HEATING  AND  VENTILATION 


to  the  bottom  and  flow  off  through  the  return.  Hot-water  radiators 
are  usually  tapped  and  plugged  so  that  the  pipe  connections  can  be 
made  either  at  the  top  or  at  the  bottom.  This  is  shown  in  Fig.  87. 

Wall  radiators  are  adapted  to  hot-water  as  well  as  steam  heating. 

Efficiency  of  Radiators.  The  efficiency  of  a  hot-water  radiator 
depends  entirely  upon  the  temperature  at  which  the  water  is  circu- 
lated. The  best  practical  results  are  obtained  with  the  water  leaving 
the  boiler  at  a  maximum  temperature  of  about  180  degrees  in  zero 
weather  and  returning  at  about  100  degrees;  this  gives  an  average 


.  si;,    r 

Prod 


mimon  Form  of  Hot-Water  Radiator.  C'ircuhiti 
iced  Wholly  through  Action  of  Gravity,  Hot 
Water  Rising  to  Top. 


Fi;,'.  87.  End  Elevation  of 
Radiator  Showing  Taps 
at  Top  and  Bottom  for 
Pipe  Connections. 


temperature  of  170  degrees  in  the  radiators.  Variations  may  be  made, 
however,  to  suit  the  existing  conditions  of  outside  temperature.  We 
have  seen  that  an  average  cast-iron  radiator  gives  off  about  1.7  B.T.U. 
per  hour  per  square  foot  of  surface  per  degree  difference  in  tempera- 
ture between  the  radiator  and  the  surrounding  air,  when  working 
under  ordinary  conditions;  and  this  holds  true  whether  it  is  filled 
with  steam  or  water. 

If  we  assume  an  average  temperature  of  170  degrees  for  the 
water,  then  the  difference  in  temperature  between  the  radiator  and 
the  air  will  be  170  —  70  =  100  degrees;  and  this  multiplied  by  1.7  = 


296 


HEATING  AND  VENTILATION 


101 


170,  which  may  be  taken  as  the  efficiency  of  a  hot- water  radiator 
under  the  above  average  conditions. 

This  calls  for  a  water  radiator  about  1 . 5  times  as  large  as  a  steam 
radiator  to  heat  a  given  room  under  the  same  conditions.  This  is 
common  practice  although  some  engineers  multiply  by  the  factor  1 . 6, 
which  allows  for  a  lower  temperature  of  the  water.  Water  leaving 
the  boiler  at  170  degrees  should  return  at  about  150;  the  drop  in 
temperature  should  not  ordinarily  exceed  20  degrees. 

Systems  of  Piping.  A  system  of  hot-water  heating  should  pro- 
duce a  perfect  circulation  of  water  from  the  heater  to  the  radiating 


Fig.  88.    System  of  Piping  Usually  Employed  for  Hot- Water  Heating. 

surface,  and  thence  back  to  the  heater  through  the  returns.  The 
system  of  piping  usually  employed  for  hot-water  heating  is  shown  in 
Fig.  88.  In  this  arrangement  the  main  and  branches  have  an  inclina- 
tion upward  from  the  heater;  the  returns  are  parallel  to  the  mains, 
and  have  an  inclination  downward  toward  the  heater,  connecting 
with  it  at  the  lowest  point..  The  flow  pipes  or  risers  are  taken  from 
the  tops  of  the  mains,  and  may  supply  one  or  more  radiators  as 
required.  The  return  risers  or  drops  are  connected  with  the  return 
mains  in  a  similar  manner.  In  this  system  great  care  must  be  taken 
to  produce  a  nearly  equal  resistance  to  flow  in  all  of  the  branches,  so 
that  each  radiator  may  receive  its  full  supply  of  water.  It  will  always 


297 


102 


HEATING  AND  VENTILATION 


be  found  that  the  principal  current  of  heated  wTater  will  take  the  path 
of  least  resistance,  and  that  a  small  obstruction  or  irregularity  in  the 
piping  is  sufficient  to  interfere  greatly  with  the  amount  of  heat  received 
in  the  different  parts  of  the  same  system. 

Some  engineers  prefer  to  carry  a  single  supply  main  around  the 
building,  of  sufficient  size  to  supply  all  the  radiators,  bringing  back 
a  single  return  of  the  same  size.  Practice  has  shown  that  in  general 
it  is  not  well  to  use  pipes  over  8  or  10  inches  in  diameter;  if  larger 
pipes  are  required,  it  is  better  to  run  two  or  more  branches. 

The  boiler,  if  possible,  should  be 'centrally  located,  and  branches 
I — |  carried  to  differ- 

ent parts  of  the 
building.  This 
insures  a  more 
even  circulation 
than  if  all  the 
radiators  are 
supplied  from  a 
single  long  main, 
in  which  case 
the  circulation 
is  liable  to  be 
sluggish  at  the 
farther  end. 

The  arrange- 
ment shown  in 
Fig.  89  is  similar 


I 


Fig.  TO.    System  of  Hot-Water   Piping   Especially    Adapted    to 
Apartment  Buildings  where  Each  Flat  Has  a  Separate  Heater. 

to  the  circuit  system  for  steam,  except  that  the  radiators  have  two 
connections  instead  of  one.  This  method  is  especially  adapted  to 
apartment  houses,  where  each  flat  has  its  separate  heater,  as  it 
eliminates  a  separate  return  main,  and  thus  reduces,  by  practically 
one-half,  the  amount  of  piping  in  the  basement.  The  supply  risers 
are  taken  from  the  top  of  the  main;  while  the  returns  should  con- 
nect into  the  side  a  short  distance  beyond,  and  in  a  direction  away 
from  the  boiler.  When  this  system  is  used,  it  is  necessary  to  enlarge 
the  radiators  slightly  as  the  distance  from  the  boiler  increases. 

In  flats  of  eight  or  ten  rooms,  the  size  of  the  last  radiator  may  be 
increased  from  10  to  15  per  cent,  and  the  intermediate  ones  proper- 


SECTIONAL    VIEW    OF    CAST    IRON    HOT    WATER    HEATER. 


HEATING  AND  VENTILATION 


103 


tionally,  at  the  same  time  keeping  the  main  of  a  large  and  uniform 
size  for  the  entire  circuit. 

Overhead  Distribution.  This  system  of  piping  is  shown  in  Fig. 
90.  A  single  riser  is  carried  directly  to  the  expansion  tank,  from 
which  branches  are  taken  to  supply  the  various  drops  to  which  the 
radiators  are  connected.  An  important  advantage  in  connection 
with  this  system  is  that  the  air  rises  at  once  to  theuexpansion  tank, 
and  escapes  through  the  vent,  so  that  air-valves  are  not  required  on 
the  radiators. 


Expa-ns'io-n  Tank 


r-irst  Floor 


TT 


Fig. 


'Overhead"  Distribution  System  of  Hot- Water  Piping. 


At  the  same  time,  it  has  the  disadvantage  that  the  water  in  the 
tank  is  under  less  pressure  than  in  the  heater;  hence  it  will  boil  at 
a  lower  temperature.  No  trouble  will  be  experienced  from  this,  how- 
ever, unless  the  temperature  of  the  water  is  raised  above  212  degrees. 

Expansion  Tank.  Every  system  for  hot-water  heating  should  be 
connected  with  an  expansion  tank  placed  at  a  point  somewhat  above 
the  highest  radiator.  The  tank  must  in  every  case  be  connected  to  a 
line  of  piping  which  cannot  by  any  possible  means  be  shut  off  from 
the  boiler.  When  water  is  heated,  it  expands  a  certain  amount, 


104 


HEATING  AND  VENTILATION 


depending  upon  the  temperature  to  which  it  is  raised*  and  a  tank  or 

reservoir  should  always  be  provided  to  care  for  this  increase  in  volume. 
Expansion  tanks  are  usually  made  of  heavy  galvanized  iron  of 

one  of  the  forms  shown  in  Figs.  91  and  92,  the  latter  form  being  used 

where  the  headroom  is  limited.  The 
connection  from  the  heating  system 
enters  the  bottom  of  the  tank,  and 
an  open  vent  pipe  is  taken  from  the 
top.  An  overflow  connected  with 
a  sink  or  drain-pipe  should  be 
provided.  Connections  should  be 
made  with  the  water  supply  both 
at  the  boiler  and  at  the  expansion 
tank,  the  former  to  be  used  when 
first  filling  the  system,  as  by  this 
means  all  air  is  driven  from  the  bot- 
tom upward  and  is  discharged 
through  the  vent  at  the  expansion 
tank.  Water  that  is  added  after- 
ward may  be  supplied  directly  to  the 

expansion  tank,  where  the  water-line  can  be  noted  in  the  gauge-glass. 

A  ball-cock  is  sometimes  arranged  to  keep  the  water-line  in  the  tank 

at  a  constant  level. 
An   alt  it  u  d  c 

(j  a  u  (j  c    is    often 

placed  in  the  base- 
ment with  the  col- 
ored hand  or  point-  c% 

er    set    to    indicate   ^ 

the   normal   water-   •• 

line   in   the  expari-   ;i  .t 

sion  tank.      When 

the    movable  hand 

falls   below  the       F 

fixed    one;    more 

water  may  be  added,  as  required,  through  the  supply  pipe  at  the  boiler. 

When  the  tank  is  placed  in  an  attic  or  roof  space  where  there  is  danger 

of  freezing,  the  expansion  pipe  may  be  connected  into  the  side  of  the 


A  Common  Form  of  G  I . 
Iron  Expansion  Tank. 


Form  of  Expansion  Tank  Used  where  Headroom 
is  Limited. 


300 


HEATING  AND  VENTILATION  105 

tank,  6  or  8  inches  from  the  bottom,  and  a  circulation  pipe  taken 
from  the  lower  part  and  connected  with  the  return  from  an  upper- 
floor  radiator.  This  produces  a  slow  circulation  through  the  tank, 
and  keeps  the  water  warm. 

The  size  of  the  expansion  tank  depends  upon  the  volume  of 
water  contained  in  the  system,  and  on  the  temperature  to  which  it  is 
heated.  The  following  rule  for  computing  the  capacity  of  the  tank 
may  be  used  with  satisfactory  results: 

Square  feet  of  radiation,  divided  by  40,  equals  required  capacity  of 
tank  in  gallons. 

Air=Venting.  One  very  important  point  to  be  kept  in  mind  in 
the  design  of  a  hot-water  system,  is  the  removal  of  air  from  the  pipes 
and  radiators.  When  the  water  in  the  boiler  is  heated,  the  air  it 
contains  forms  into  small  bubbles  which  rise  to  the  highest  points  of  the 
system. 

In  the  arrangement  shown  in  Fig.  88,  the  main  and  branches 
grade  upward  from  the  boiler,  so  that  the  air  finds  its  way  into  the 
radiators,  from  which  it  may  be  drawn  off  by  means  of  the  air-valves. 

A  better  plan  is  that  shown  in  Fig.  89.  In  this  case  the  expan- 
sion pipe  is  taken  directly  off  the  top  of  the  main  over  the  boiler,  so 
that  the  larger  part  of  the  air  rises  directly  to  the  expansion  tank  and 
escapes  through  the  vent  pipe.  The  same  action  takes  place  in  the 
overhead  system  shown  in  Fig.  90,  where  the  top  of  the  main  riser 
is  connected  with  the  tank.  Every  high  point  in  the  system  and 
every  radiator,  except  in  the  downward  system  with  top  supply  con- 
nection, should  be  provided  with  an  air-valve. 

Pipe  Connections.  There  are  Various  methods  of  connecting 
the  radiators  with  the  mains  and  risers.  Fig.  93  shows  a  radiator 
connected  with  the  horizontal  flow  and  return  mains,  which  are 
located  below  the  floor.  The  manner  of  connecting  with  a  vertical 
riser  and  return  drop  is  shown  in  Fig.  94.  As  the  water  tends  to 
flow  to  the  highest  point,  the  radiators  on  the  lower  floors  should  be 
favored  by  making  the  connection  at  the  top  of  the  riser  and  taking 
the  pipe  for  the  upper  floors  from  the  side  as  shown.  Fig.  95  illus- 
trates the  manner  of  connecting  with  a  radiator  on  an  upper  floor  where 
the  supply  is  connected  at  the  top  of  the  radiator. 

The  connections  shown  in  Figs.  96  and  97  are  used  with  the 
overhead  system  shown  in  Fig.  90. 


301 


100 


HEATING  AND  VENTILATION 


Where  the  connection  is  of  the  form  shown  at  the  left  in  Fig.  90, 
the  cooler  water  from  the  radiators  is  discharged  into  the  supply  pipe 
again,  so  that  the  water  furnished  to  the  radiators  on  the  lower  floors 
is  at  a  lower  temperature,  and  the  amount  of  heating  surface  must  be 
correspondingly  increased  to  make  up  for  this  loss,  as  already  de- 
scribed for  the  circuit  system. 


"ig  93     Radiator    Connected    with   Hori- 
zontal Flow  and  Return  Mains 
Located  below  Floor. 


Fig.  94.    Radiator  Connected  to  Vertical 
Riser  and  Return  Drop. 


For  example,  if  in  the  case  of  Fig.  90  we  assume  the  water  to 
leave  at  180  degrees  and  return  at  160,  we  shall  have  a  drop  in  tem- 
perature of  10  degrees  on  each  floor;  that  is,  the  water  will  enter  the 
radiator  on  the  second  floor  at  ISO  degrees  and  leave  it  at  170,  and 
will  enter  the  radiator  on  the  first  floor  at  170  and  leave  it  at  160. 


'pper-Floor  Radiator  with  Sup- 
ply Connected  at  Top. 


Fig  96.    Radiator  Connections,  Overhead 
Distribution  System. 

The  average  temperatures  will  be  175  and  165,  respectively.  The 
efficiency  in  the  first  case  will  be  175  —  70  =  105;  and  105  X  1.5  = 
157.  In  the  second  case,  165  —  70  =  95;  and  95  X  1.5  =  142; 
so  that  the  radiator  on  the  first  floor  will  have  to  be  larger  than  that 
on  the  second  floor  in  the  ratio  of  157  to  142,  in  order  to  do  the  same 
work. 


302 


HEATING  AND  VENTILATION 


107 


This  is  approximately  an  increase  of  10  per  cent  for  each  story 
downward  to  offset  the  cooling  effect;  but  in  practice  the  supply 
drops  are  made  of  such  size  that  only  a  part  of  the  water  is  by-passed 
through  the  radiators.  For  this  reason  an  increase  of  5  per  cent 
for  each  story  downward  is  probably  sufficient  in  ordinary  cases. 

Where  the  radiators  discharge 
into  a  separate  return  as  in  the  case 
of  Fig.  88,  or  those  at  the  right  in 
Fig.  90,  we  may  assume  the  tempera- 
ture of  the  water  to  be  the  same  on 
all  floors,  and  give  the  radiators  an 
equal  efficiency. 

In  a  dwelling-house  of  two  stories, 
no  difference  would  be  made  in  the 
sizes  of  radiators  on  the  two  floors; 
but  in  the  case  of  a  tall  office  build- 
ing, corrections  would  necessarily  be  made  as  above  described. 

Where  circulation  coils  are  used,  they  should  be  of  a  form  which 
will  tend  to  produce  a  flow  of  water  through  them.  Figs.  98,  99,  and 
100  show  different  ways  of  making  up  and  connecting  these  coils. 
In  Figs.  98  and  100,  supply  pipes  may  be  either  drops  or  risers;  and 


Pig.  97.    Another  Form   of   Radiator 
Connection,  Overhead  Distribu- 
tion System. 


fc 


8 


Fig.  98.    Circulation  Coil,  One  Method  of  Construction.    Supply  Pipes 
may  be  Either  Drops  or  Risers. 

in  the* former  case  the  return  in  Fig.  100  may  be  carried  back,  if  desired, 
into  the  supply  drop,  as  shown  by  the  dotted  lines. 

Combination  Systems.  Sometimes  the  boiler  and  piping  are 
arranged  for  either  steam  or  hot  water,  since  the  demand  for  a  higher 
or  lower  temperature  of  the  radiators  might  change. 


303 


108 


HEATIXG  AND  VENTILATION 


The  object  of  this  arrangement  is  to  secure  the  advantages  of  a 
hot-water  system  for  moderate  temperatures,  and  of  steam  heating 
for  extremely  cold  weather. 


Fig.  99.    Another  Method  of  Building  Up  a  Circulation  Coil. 

As  less  radiating  surface  is  required  for  steam  heating,  there  is 
an  advantage  due  to  the  reduction  in  first  cost.  This  is  of  consider- 
able importance,  as  a  heating  system  must  be  designed  of  such  dimen- 
sions as  to  be  capable  of  warming  a  building  in  the  coldest  weather; 

LJ 


GjUl/U            :                                                             11  N 

r?  J 

^n 

U^ 

;  & 

VU 

1T> 

n5  ) 

'fl 

Ix 

(  £ 

VU 

1N 

n>  ) 

'  :;    ^J 

fl  J 

Fig.  100.    Circulation  Coil  with  Either  Drop  or  Riser  Supply.     In  former  case,  return 
may  !><>  carried  into  Supply  Drop  as  shown  by  "Dotted  Lines. 

and  this  involves  the  expenditure  of  a  considerable  amount  for  radiat- 
ing surfaces,  which  are  needed  only  at  rare  intervals.  A  combination 
system  of  hot-water  and  steam  heating  requires,  first,  a  heater  or  boiler 


304 


HEATING  AND  VENTILATION  109 


which  will  answer  for  either  purpose;  second,  a  system  of  piping 
which  will  permit  the  circulation  of  either  steam  or  hot  water;  and 
third,  the  use  of  radiators  which  are  adapted  to  both  kinds  of  heating. 
These  requirements  will  be  met  by  using  a  steam  boiler  provided  with 
all  the  fittings  required  for  steam  heating,  but  so  arranged  that  the 
damper  regulator  may  be  closed  by  means  of  valves  when  the  system 
is  to  be  used  for  hot-water  heating.  The  addition  of  an  expansion 
tank  is  required,  which  must  be  so  arranged  that  it  can  be  shut  off 
when  the  system  is  used  for  steam  heating.  The  system  of  piping 
shown  in  Fig.  88  is  best  adapted  for  a  combination  system,  although 
an  overhead  distribution  as  shown  in  Fig.  90  may  be  used  by  shutting 
off  the  vent  and  overflow  pipes,  and  placing  air-valves  on  the  radiators. 

While  this  system  has  many  advantages  in  the  way  of  cost  over 
the  complete  hot- water  system,  the  labor  of  changing  from  steam 
to  hot  water  will  in  some  cases  be  trouble- 
some; and  should  the  connections  to  the 
expansion  tank  not  be  opened,  serious  re- 
sults would  follow. 

Valves  and  Fittings.  Gate-valves 
should  always  be  used  in  connection  with 
hot-water  piping,  although  angle-valves  may 
be  used  at  the  radiators.  There  are  several 
patterns  of  radiator  valves  made  especially 
for  hot-water  work;  their  chief  advantage 

lies  in  a  device  -for  quick  closing,  usually  a  Flg.  101>  Radlator  Valve  for 
quarter-turn  or  half-turn  being  sufficient  to 

open  "or  close  the  valve.  Two  different  designs  are  shown  in  Figs. 
101  and  102. 

It  is  customary  to  place  a  valve  in  only  one  connection,  as  that  is 
sufficient  to  stop  the  flow  of  water  through  the  radiator;  a  fitting 
known  as  a  union  elbow  is  often  employed  in  place  of  the  second  valve. 
(See  Fig.  103.) 

Air=Valves.  The  ordinary  pet-cock  air-valve  is  the  most  reliable 
for  hot-water  radiators,  although  there  are  several  forms  of  auto- 
matic valves  which  are  claimed  to  give  satisfaction.  One  of  these 
is  shown  in  Fig.  104.  This  is  similar  in  construction  to  a  steam 
trap.  As  air  collects  in  the  chamber,  and  the  water-line  is  lowered, 
the  float  drops,  and  in  so  doing  opens  a  small  valve  at  the  top  of  the 


305 


110 


HEATING  AND  VENTILATION 


chamber,  which  allows  the  air  to  escape.     As  the  water  flows  in  to  take 
its  place,  the  float  is  forced  upward  and  the  valve  is  closed. 

All  radiators  which  are  supplied  by  risers  from  below,  should  be 
provided  with  air-valves  placed  in  the  top 
of  the  last  section  at  the  return  end.  .  If 
they  are  supplied  by  drops  from  an  over- 


rig.  102.    Another  Type  of  Hot- 
Water  Radiator  Valve. 


Fig.  103.    Union  Elbow. 


head  system,  the  air  wrill  be  discharged  at  the   expansion  tank,  and 

air-valves  will  not  be  necessary  at  the  radiators. 

Fittings.     All  fittings,  such  as  elbows,  tees,  etc.,  should  be  of 

the  long-turn  pattern.  If  the  common  form  is  used,  they  should  be 
a  size  larger  than  the  pipe,  bushed 
down  to  the  proper  size.  The  long- 
turn  fittings,  however,  are  preferable, 
and  give  a  much  better  appearance. 
Connections  between  the  radiators 
and  risers  may  'be  made  with  the 
ordinary  short-pattern  fittings,  as 
those  of  the  other  form  are  not  \vell 
adapted  to  the  close  connections  nec- 
essary for  this  work. 

Pipe  Sizes.  The  size  of  pipe 
required  to  supply  any  given  radiator 
depends  upon  four  conditions ;  first,  the 
size  of  the  radiator;  second,  its  elevation 
above  the  boiler;  third,  the  length  of 
pipe  required  to  connect  it  with  the 

boiler;  and  fourth,  the  difference  in  temperature  between  the  supply 

and  the  return, 


Hot-Water  Radiator.    Operated 
by  a  Float. 


306 


HEATING  AND  VENTILATION 


111 


As  it  would  be  a  long  and  rather  complicated  process  to  work  out 
the  required  size  of  each  pipe  for  a  heating  system,  Tables  XXVI  and 
XXVII  have  been  prepared,  covering  the  usual  conditions  to  be  met 
with  in  practice. 

TABLE   XXVI 

Direct  Radiating  Surface  Supplied  by  Mains  of  Different 
Sizes  and  Lengths  of  Run 


SQUARE  FEET  OP   RADIATING   SURFACE 


100  ft. 
Run 

200    ft. 
Run 

300   ft. 
Run 

400    ft. 
Run 

500  ft. 
Run 

600   ft 
Run 

700   ft. 
Run 

800  ft. 
Run 

1,000 
ft.  Run 

1    in. 

30 

H' 

60 

50 

l!' 

100 

75 

50 

2    ' 

200 

150 

125 

100 

75 

2*' 

350 

250 

200 

175 

150 

125 

3    ' 

550 

400 

300 

275 

250 

225 

200 

175 

150 

3i' 

850 

600 

450 

400 

350 

325 

300 

250 

225 

4    ' 

1,200 

850 

700 

600 

525 

475 

450 

400 

350 

5    ' 

1,400 

1,150 

1,000 

700 

850 

775 

725 

650 

6    ' 

1,600 

1,400 

1,300 

1,200 

1,150 

1,000 

7    ' 

1,706 

1,600 

1,500 

These  quantities  have  been  calculated  on  a  basis  of  10  feet  difference 
in  elevation  between  the  center  of  the  heater  and  the  radiators,  and  a  differ- 
ence in  temperature  of  17  degrees  between  the  supply  and  the  return. 

TABLE   XXVII 

Radiating  Surface  on  Different  Floors  Supplied  by 
Pipes  of  Different  Sizes 


SIZE  OF 


SQUARE  FEET  OF  RADIATING   SURFACE 


1st    Story 

2d   Story 

3d   Story 

4th  Story 

5th  Story 

6th  Story 

1     in. 

30 

55 

65 

75 

85 

95 

1M  ' 

60 

90 

110 

125 

140 

160 

iy2  ' 

100 

140 

165 

185 

210 

240 

2      < 

200 

275 

375 

425 

500 

2^' 

350 

-475 

3      ' 

550 

•   __ 

sy2' 

850 

Table  XXVI  gives  the  number  of  square  feet  of  direct  radiation 
which  different  sizes  of  mains  and  branches  will  supply  for  varying 
lengths  of  run. 

Table  XXVI  may  be  used  for  all  horizontal  mains.  For  vertical 
risers  or  drops,  Table  XXVII  may  be  used.  This  has  been  com- 


307 


HEATING  AND  VENTILATION 


puted  for  the  same  difference  in  temperature  as  in  the  case  of  Table 
XXVI  (17  degrees),  and  gives  the  square  feet  of  surface  which  dif- 
ferent sizes  of  pipe  will  supply  on  the  different  floors  of  a  building, 
assuming  the  height  of  the  stories  to  be  10  feet.  Where  a  single 
riser  is  carried  to  the  top  of  a  building  to  supply  the  radiators  on  the 
floors  below,  by  drop  pipes,  we  must  first  get  what  is  called  the  average 
elevation  of  the  system  before  taking  its  size  from  the  table.  This  may 
be  illustrated  by  means  of  a  diagram  (see  Fig.  105). 

In  .1  we  have  a  riser  carried  to  the  third  story,  and  from  there  a 
drop  brought  down  to  supply  a  radiator  on  the  first  floor.  The 
elevation  available  for  producing  a  flow  in  the  riser  is  only  10  feet, 
the  same  as  though  it  extended  only  to  the  radiator.  The  water  in 
the  two  pipes  above  the  radiator  is  practically  at  the  same  temperature, 
and  therefore  in  equilibrium,  and  has  no  effect  on  the  flow  of  the 
water  in  the  riser.  (Actually  there  would  be  some  radiation  from  the 
pipes,  and  the  return,  above  the  radiator,  would  be  slightly  cooler,  but 
for  purposes  of  illustration  this  may  be  neglected).  If  the  radiator 
was  on  the  second  floor  the  elevation  of  the  system  would  be  20  feet 
(see  B};  and  on  the  third  floor,  30  feet;  and  so  on.  The  distance 
which  the  pipe  is  carried  above  the  first  radiator  which  it  supplies 
has  but  little  effect  in  producing  a  flow,  especially  if  covered,  as  it 
should  be  in  practice.  Having  seen  that  the  flow  in  the  main  riser 
depends  upon  the  elevation  of  the  radiators,  it  is  easy  to  see  that  the 
way  in  which  it  is  distributed  on  the  different  floors  must  be  con- 
sidered. For  example,  in  B,  Fig.  105,  there  will  be  a  more  rapid 
flow  through  the  riser  with  the  radiators  as  shown,  than  there  would 
be  if  they  were  reversed  and  the  largest  one  were  placed  upon  the  first 
floor. 

We  get  the  average  elevation  of  the  system  by  multiplying  the 
square  .feet  of  radiation  on  each  floor  by  the  elevation  above  the 
heater,  then  adding  these  products  together  and  dividing  the  same 
by  the  total  radiation  in  the  whole  system.  In- the  case  shown  in 
B,  the  average  elevation  of  the  system  would  be 
(100  X  30)  +  (-50  X  20)  +  (25  X  10)  = 

100  +  50  +  25 

and  we  must  proportion  the  main  riser  the  same  as  though  the  whole 
radiation  were  on  the  second  floor.  Looking  in  Table  XXVII,  we 
find,  for  the  second  story,  that  a  l-|-inch  pipe  will  supply  140  square 


308 


HEATING  AND  VENTILATION 


113 


fc-ct;  and  a  2-inch  pipe,  275  feet.     Probably  a  1^-inch  pipe  would 
be  sufficient. 

Although  the  height  of  stories  varies  in  different  buildings,  10 
feet  will  be  found  sufficiently  accurate  for  ordinary  practice. 

INDIRECT  HOT=WATER  HEATING 

This  is  used  under  the  same  conditions  as  indirect  steam,  and 
the  heaters  used  are  similar  to  those  already  described.     Special 


3= I 


A  B 

Fig.  105.    Diagram  to  Illustrate  Finding  of  Average  Elevation  of  Heating  System. 

attention  is  given  to  the  form  of  the  sections,  in  order  that  there  may 
be  an  even  distribution  of  water  through  all  parts  of  them.  As  the 
stacks  are  placed  in  the  basement  of  a  building,  and  only  a  short 
distance  above  the  boiler,  extra  large  pipes  must  be  used  to  secure  a 
proper  circulation,  for  the  head  producing  flow  is  small.  The  stack 


309 


114  HEATING  AND  VENTILATION 

casings,  cold-air  and  warm-air  pipes,  and  registers  are  the  same  as 
in  steam  heating. 

Types  of  Radiators.  The  radiators  for  indirect  hot-water  heating 
are  of  the  same  general  form  as  those  used  for  steam.  Those  shown 
in  Figs.  52,  53,  5G,  106,  and  107  are  common  patterns.  The  drum 
pin,  Fig.  106,  is  an  excellent  form,  as  the  method  of  making  the 
connections  insures  a  uniform  distribution  of  water  through  the 
stack. 

Fig.  107  shows  a  radiator  of  good  form  for  water  circulation,  and 
also  of  good  depth,  which  is  a  necessary  point  in  the  design  of  hot- 
water  radiators.  They  should  be  not  less  than  12  or  15  inches  deep 
for  good  results.  Box  coils  of  the  form  given  for  steam  may  also  be 


Fip.  10(5.    "Drum  Pin"  Indirect  Hot-Water  Radiator. 

used,  provided  the  connections  for  supply  and  return  are  made  of 
good  size. 

Size  of  Stacks.  As  indirect  hot-water  heaters  are  used  princi- 
pally in  the  warming  of  dwelling-houses,  and  in  combination  with 
direct  radiation,  the  easiest  method  is  to  compute  the  surfaces  required 
for  direct  radiation,  and  multiply  these  results  by  1 .5  for  pin  radiators 
of  good  depth.  For  other  forms  the  factor  should  vary  from  1.5 
to  2,  depending  upon  the  depth  and  proportion  of  free  area  for  air- 
flow between  the  sections. 

If  it  is  desired  to  calculate  the  required  surface  directly  by  the 
thermal  unit  method,  we  may  allow  an  efficiency  of  from  360  to  400 
for  good  types  in  zero  weather. 


310 


HEATING  AND  VENTILATION 


In  schoolhouse  and  hospital  work,  where  larger  volumes  of  air 
are  warmed  to  lower  temperatures,  an  efficiency  as  high  as  500  B.  T.  U. 
may  be  allowed  for  radiators  of  good  form. 

Flues  and  Casings.  For  cleanliness,  as  well  as  for  obtaining 
the  best  results,  indirect  stacks  should  be  hung  at  one  side  of  the 
register  or  flue  receiving  the  warm  air,  and  the  cold-air  duct  should 
enter  beneath  the  heater  at  the  other  side.  A  space  of  at  least  10 
inches,  and  preferably  12,  should  be  allowed  for  the  warm  air  above 
the  stack.  The  top  of  the  casing  should  pitch  upward  toward  the 
warm-air  outlet  at  least  an  inch  in  its  length.  A  space  of  from  8  to 
10  inches  should  be  allowed  for  cold  air  below  the  stack. 

As  the  amount  of  air  warmed  per  square  foot  of  heating  surface 
is  less  than  in  the  case  of  steam,  we  may  make  the  flues  somewhat 
smaller  as  compared 
with  the  size  of  heater. 
The  following  p  r  o  - 
portions  may  be  used 
under  usual  conditions 
for  dwelling  -  houses : 
l£  square  inches  per 
square  foot  of  radia- 
tion for  the  first  floo*-, 
lj  square  inches  for 
the  second  floor,  and 
1£  square  inches  for 
the  cold-air  duct. 

Pipe  Connections.  In  indirect  hot-water  work,  it  is  not  desirable 
to  supply  more  than  80  to  100  square  feet  of  radiation  from  a  single 
connection.  When  the  requirements  call  for  larger  stacks,  they 
should  be  divided  into  two  or  more  groups  according  to  size. 

It  is  customary  to  carry  up  the  main  from  the  boiler  to  a  point 
near  the  basement  ceiling,  where  it  is  air- vented  through  a  small 
pipe  leading  to  the  expansion  tank.  The  various  branches  should 
grade  downward  and  connect  with  the  tops  of  the  stacks.  In  this 
way,  all  air,  both  from  the  boiler  and  from  the  stacks,  will  find  its  way 
to  the  highest  point  in  the  main,  and  be  carried  off  automatically. 

As  an  additional  precaution,  a  pet-cock  air-valve  should  be  placed 
in  the  last  section  of  each  stack,  and  brought  out  through  the  casing 
by  means  of  a  short  pipe. 


Fig.  107.    Indirect  Hot- Water  Radiator. 


311 


IK) 


HEATING  AND  VENTILATION 


TABLE   XXVIII 

Radiating  Surface  Supplied  by  Pipes  of  Various   Sizes— Indirect  Hot= 
Water  System 


SQCAKK   FEET    or   RAWATINO   SI'HFACE 


100  Ft.  Hun 


1  in.          15 

H  '•          30 

25 

H  " 

50 

40 

25 

2"  •'      100 

75 

60 

2i  " 

175 

125 

100 

3"  " 

275 

200 

150 

34  " 

425 

300 

225 

4  " 

GOO 

425 

350 

5  " 

700 

575 

(i  '• 

7  '' 

50 
90 

140 
200 
300 
500 
800 
1,200 


Some  engineers  make  a  practice  of  carrying  the  main  to  the 
ceiling  of  the  first  story,  and  then  dropping  to  the  basement  before 
branching  to  the  stacks,  the  idea  being  to  accelerate  the  flow  of  water 
through  the  main,  which  is  liable  to  be  sluggish  on  account  of  the 
small  difference  in  elevation  between  the  boiler  and  stacks.  If 
the  return  leg  of  the  loop  is  left  uncovered,  there  will  be  a  slight  drop 
in  temperature,  tending  to  produce  this  result;  but  in  any  case  it  will 
be  exceedingly  small.  With  supply  and  return  mains  of  suitable 
size  and  properly  graded,  there  should  be  no'difficulty  in  securing  a 
good  circulation  in  basements  of  average  height. 

Pipe  Sizes.  As  the  difference  in  elevation  between  the  stacks 
and  the  heater  is  necessarily  small,  the  pipes  should  be  of  ample  size 
to  offset  the  slow  velocity  of  flow  through  them.  The  sizes  mentioned 
in  Table  XXVIII,  for  runs  up  to  400  feet,  will  be  found  to  supply 
ample  radiating  surface  for  ordinary  conditions.  Some  engineers 
make'  a  practice  of  using  somewhat  smaller  pipes,  but  the  larger  sizes 
will  in  general  be  found  more  satisfactory. 

CARE  AND   MANAGEMENT  OF  HOT=WATER  HEATERS 

The  directions  given  for  the  care  of  steam-heating  boilers  apply 
in  a  general  way  to  hot-water  heaters,  as  to  the  methods  of  caring 
for  the  fires  and  for  cleaning  and  filling  the  heater.  Only  the  special 
points  of  difference  need  be  considered.  Before  building  the  fire,  all 
the  pipes  and  radiators  must  be  full  of  water,  and  the  expansion  tank 


312 


HEATING  AND  VENTILATION 


117 


should  be  partially  filled  as  indicated  by  the  gauge-glass.  Should 
the  water  in  any  of  the  radiators  fail  to  circulate,  see  that  the  valves 
are  wide  open  and  that  the  radiator  is  free  from  air.  Water  must 
always  be  added  at  the  expansion  tank  when  for  any  reason  it  is 
drawn  from  the  system. 

The  required  temperature  of  the  water  will  depend  upon  the 
outside  conditions,  and  only  enough  fire  should  be  carried  to  keep 
the  rooms  comfortably  warm.  Ther- 
mometers should  be  placed  in  the  flow 
and  return  pipes  near  the  heater,  as  a 
guide.  Special  forms  are  made  for 
this  purpose,  in  which  the  bulb  is  im- 
mersed in  a  bath  of  oil  or  mercury  (see. 
Fig.  108). 

FORCED    HOT=WATER    CIRCU= 
LATION 

While  the  gravity  system  of  hot- 
water  heating  is  well  adapted  to 
buildings  of  small  and  medium  size, 
there  is  a  limit  to  which  it  can  be  car- 
ried economically.  This  is  due  to  the 
slow  movement  of  the  water,  which 
calls  for  pipes  of  excessive  size.  To 
overcome  this  difficulty,  pumps'  are 
used  to  force  the  water  through  the 
mains  at  a  comparatively  high  velocity. 

The  water  may  be  heated  in  a 
boiler  in  the  same  manner  as  for 
gravity  circulation,  or  exhaust  steam 
may  be  utilized  in  a  feed-water  heater 
of  large  size.  Sometimes  part  of  the 
heat  is  derived  from  an  economizer  placed  in  the  smoke  passage 
from  the  boilers. 

Systems  of  Piping.  The  mains  for  forced  circulation  are  usually 
run  in  one  of  two  ways.  In  the  two-pipe  system,  shown  in  Fig.  109, 
the  supply  and  return  are  carried  side  by  side,  the  former  reducing 
in  size,  and  the  latter  increasing  as  the  branches  are  taken  off. 


.  108.    Thermometer  Attached  to 
jed-Pips  near  Heater,  to  Deter- 
mine Temperature  of  Water. 


313 


118 


HEATING^AND  VENTILATION 


The  flow  through  the  risers  is  produced  by  the  difference  in 
pressure  in  the  supply  and  return  mains;  and  as  this  is  greatest 
nearest  the  pump,  it  is  necessary  to  place  throttle-valves  in  the  risers 
to  prevent  short-circuiting  and  to  secure  an  even  distribution  through 
all  parts  of  the  system. 

Fig.  110  shows  the  single-pipe  or  circuit  system.  This  is  similar 
to  the  one  already  described  for  gravity  circulation,  except  that  it  can 
be  used  on  a  much  larger  scale. 

A  single  main  is  carried  entirely  around  the  building  in  this 
case,  the  ends  being  connected  with  the  suction  and  discharge  of  the 
pump  as  shown. 

As  the  pressure  or  head  in  the  main  drops  constantly  throughout 
the  circuit,  from  the  discharge  of  the  pump  back  to  the  suction,  it  is 


Fig.  109.     "Two-Pipe"  System  for  Forced  Hot-Water  Circulation. 


evident  that  if  a  supply  riser  be  taken  off  at  any  point,  and  the  return 
be  connected  into  the  main  a  short  distance  along  the  line,  there  will 
be  a  .sufficient  difference  in  pressure  between  the  two  points  to  produce 
a  circulation  through  the  two  risers  and  the  connecting  radiators. 
A  distance  of  8  or  10  feet  between  the  connections  is  usually  ample  to 
produce  the  necessary  circulation,  and  even  less  if  the  supply  is  taken 
from  the  top  of  the  main  and  the  return  connected  into  the  side. 

Sizes  of  Mains  and  Branches.  As  the  velocity  of  flow  is  inde- 
pendent of  the  temperature  and  elevation  when  a  pump  is  used,  it  is 
necessary  to  consider  only  the  volume  of  water  to  be  moved  and  the 
length  of  run. 


314 


TYPICAL    HEATING    INSTALLATION    SHOWING    SECTIONAL    BOILER 
AND    RADIATOR. 

American  Radiator  Company. 


HEATING  AND  VENTILATION 


119 


The  volume  is  found  by  the  equation 

Q-    K  E 

y  ~  500  7" 
in  which 

Q  =  Gallons  of  water  required  per  minute; 
R  —  Square  feet  of  radiating  surface  to  be  supplied; 
E  —  Efficiency  of  radiating  surface  in  B.  T.  U.  per  sq.  foot  per  hour; 
T  —  Drop  in  temperature  of  the  water  in  passing  through  the  heating 
system. 

In  systems  of  this  kind,  where  the  circulation  is  comparatively 
rapid,  it  is  customary  to  assume  a  drop  in  temperature  of  30°  to  40°, 
between  the  supply  and  return. 

Having  determined  the  gallons  of  water  to  be  moved,  the  required 
size  of  main  can  be  found  by  assuming  the  velocity  of  flow,  which 
for  pipes  from  5  to  8  inches  in  diameter  may  be  taken  at  400  to  500 


Fig.  110.    "Single-Pipe"  or  "Circuit"  System  for  Forced  Hot- Water  Circulation. 

feet  per  minute.  A  velocity  as  high  as  600  feet  is  sometimes  allowed 
for  pipes  of  large  size,  while  the  velocity  in  those  of  smaller  diameter 
should  be  proportionally  reduced  to  250  or  300  feet  for  a  3-inch  pipe. 
The  next  step  is  to  find  the  pressure  or  head  necessary  to  force  the 
water  through  the  main  at  the  given  velocity.  This  in  general  should 
not  exceed  50  or  60  feet,,  and  much  better  pump  efficiencies  will  be 
obtained  with  heads  not  exceeding  35  or  40  feet. 

As  the  water  in  a  heating  system  is  in  a  state  of  equilibrium,  the 
only  power  necessary  to  produce  a  circulation  is  that  required  to 
overcome  the  friction  in  the  pipes  and  radiators;  and,  as  the  area  of 
the  passageways  through  the  latter  is  usually  large  in .  comparison 
with  the  former,  it  is  customary  to  consider  only  the  head  necessary 
to  force  the  water  through  the  mains,  taking  into  consideration  the 
additional  friction  produced  by  valves  and  fittings. 


315 


120  HEATING  AND  VENTILATION 

Each  Ions-turn  elbow  may  be  taken  as  adding  about  4  feet  to 
the  length  of  pipe;  a  short-turn  fitting,  about  9  feet;  6-inch  and 
4-inch  swing  check-valves,  -50  feet  and  25  feet,  respectively;  and 
6-inch  and  4-inch  globe  check-valves.  200  feet  and  130  feet,  respec- 
tively. 

Table  XXIX  is  prepared  especially  for  determining  the  size  of 
mains  for  different  conditions,  and  is  used  as  follows: 

Ex<i»-pif.  Suppose  that  a  heating  system  requires  the  circulation  of  480 
gallons  of  water  per  minute  through  a  circuit  main  600  feet  in  length.  The 
pipe  contains  12  long-turn  elbows  and  1  swing  check-valve.  What  diameter 
of  main  should  be  used  ? 

Assuming  a  velocity  of  4SO  feet  per  minute  as  a  trial  velocity,  we 
follow  along  the  line  corresponding  to  that  velocity,  and  find  that  a 
5-inch  pipe  will  deliver  the  required  volume  of  water  under  a  head 
of  4.0  feet  for  each  100  feet  length  of  run. 

The  actual  length  of  the  main,  including  the  equivalent  of  the 
fittings  as  additional  length,  is 

600  -    12  X  9  i  —  50  =  75S  feet ; 

hence  the  total  head  required  is  4.9  X  7.5S  =  37  feet.  As  both 
the  assumed  velocity  and  the  necessary  head  come  within  practicable 
limits,  this  is  the  size  of  pipe  which  would  probably  be  used.  If  it 
were  desired  to  reduce  the  power  for  running  the  pump,  the  size  of 
main  could  be  increased.  That  is.  Table  XXIX  shows  that  a  6-inch 
pipe  would  deliver  the  same  volume  of  water  with  a  friction  head  of 
only  about  2  feet  per  100  feet  in  length,  or  a  total  head  of  2  /  7.5S  = 
15  feet. 

The  risers  in  the  circuit  system  are  usually  made  the  same  size 
as  for  gravity  work  With  double  mains,  as  shown  in  Fig.  109,  they 
may  be  somewhat  smaller,  a  reduction  of  one  size  for  diameters  over 
1^  inches  being  common 

The  branches  connecting  the  risers  with  the  mains  may  be  pro- 
portioned from  the  combined  areas  of  the  risers,  ^"hen  the  branches 
are  of  considerable  size,  the  diameter  may  be  computed  from  the 
available  head  and  volume  of  water  to  be  moved. 

Pumps.  Centrifugal  pumps  are  usually  employed  in  connection 
with  forced  hot-water  circulation,  in  preference  to  pumps  of  the 
piston  or  plunger  type.  They  are  simple  in  construction,  having 
BO  valves,  produce  a  continuous  flow  of  water,  and,  for  the  low  heads 


316 


HEATING  AND  VENTILATION 


121 


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122  HEATING  AND  VENTILATION 

against  which  they  are  operated,  have  a  good  efficiency.     A  pump  of 
this  type,  with  a  direct-connected  engine,  is  shown  in  Fig.  111. 

Under  ordinary  conditions  the  efficiency  of  a  centrifugal  pump 
falls  off  considerably  for  heads  above  30  or  35  feet;  but  special  high- 
speed pumps  are  constructed  which  work  with  a  good  efficiency 
against  500  feet  or  more. 

Under  favorable  conditions  an  efficiency  of  60  to  70  per  cent  is 
often  obtained;  but  for  hot-water  circulation  it  is  more  common  to 
assume  an  efficiency  of  about  50  per  cent  for  the  average  case. 

The  horse-power  required  for  driving  a  pump  is  given  by  the 
following  formula : 

_  Hx  VX  8.3 
"     33,OOOX#' 
in  which 

H  =  Friction  head  in  feet; 

V  —  Gallons  of  water  delivered  per  minute; 

E  =  Efficiency  of  pump. 

Centrifugal  pumps  are  made  in  many  sizes  and  with  varying 
proportions,  to  meet  the  different  requirements  of  capacity  and  head. 

Heaters.  If  the  water  is  heated  in  a  boiler,  any  good  form  may 
be  used,  the  same  as  for  gravity  work.  In  case  tubular  boilers  are 
used,  the  entire  shell  may  be  rilled  with  tubes,  as  no  steam  space  is 
required. 

In  order  to  prevent  the  water  from  passing  in  a  direct  line  from 
the  inlet  to  the  outlet,  a  series  of  baffle-plates  should  be  used  to  bring 
it  in  contact  with  all  parts  of  the  heating  surface. 

When  steam  is  used  for  heating  the  water,  it  is  customary  to 
employ  a  closed  feed-water  heater  with  the  steam  on  the  inside  of  the 
tubes  and  the  water  on  the  outside. 

Any  good  form  of  heater  can  be  used  for  this  purpose  by  providing 
it  with  steam  connections  of  sufficient  size.  In  the  ordinary  form  of 
heater,,  the  feed-water  flows  through  the  tubes,  and  the  connections 
are  therefore  small,  making  it  necessary  to  substitute  special  nozzles 
of  large  size  when  used  in  the  manner  here  described. 

When  computing  the  required  amount  of  heating  surface  in  the 
tubes  of  a  heater,  it  is  customary  to  assume  an  efficiency  of  about  200 
B-  T.  U.  per  square  foot  of  surface  per  hour,  per  degree  difference  in 
temperature  between  the  water  and  steam. 


818 


HEATING  AND  VENTILATION 


123 


It  is  usual  to  circulate  the  water  at  a  somewhat  higher  tempera- 
ture in  systems  of  this  kind,  and  a  maximum  initial  temperature  of 
200  degrees,  with  a  drop  of  40  degrees  in  the  heating  system,  may  be 
used  in  computing  the  size  of  heater.  If  exhaust  steam  is  used  at 
atmospheric  pressure,  there  will  be  a  difference  of  212  —  180  =  32 
degrees,  between  the  average  temperature  of  the  water  and  the  steam , 
giving  an  efficiency  of  200  X  32  -  6,400  B.  T.  U.  per  square  foot 
of  heating  surface. 

From  this  it  is  evident  that  6,400  •*•  170  =  38  square  feet  of 
direct  radiating  surface,  or  6,400  -f-  400  =  16  square  feet  of  indirect, 
may  be  supplied  from  each  square  foot  of  tube  surface  in  the  heater. 
Example.  A  building  having  6,000  square  feet  of  direct;  and  2,000 
square  feet  of  indirect  radiation,  is  to  be  warmed  by  hot  water  under  forced 
circulation.  Steam  at  atmospheric  pressure  is  to  be  used  for  heating  the 
water.  How  many  square  feet  of  heating  surface  should  the  heater  contain  ? 

6,000  -=-  38  =  158;  and  2,000 
-=-  16  =  125;  therefore,  158  + 
125  =  283  square  feet,  the  area 
of  heating  surface  called  for. 

When  the  exhaust  steam  is 
not  sufficient  for  the  require- 
ments, an  auxiliary  live  steam 
heater  is  used  in  connection 
with  it. 

EXAMPLES  FOR  PRACTICE 

1.  A   building   contains 
10,000    square     feet     of    direct 
radiation  and  4,000  square  feet 
of     indirect     radiation.       How 

many  gallons  of  water  must  be  circulated  through  the  mains  per  min- 
ute, allowing  a  drop  in  temperature  of  40  degrees?  Axs.  165 .gal. 

2.  In  the  above  example,  what  size  of  main  should   be  used, 
assuming  the  circuit  to  be  300  feet  in  length  and  to  contain  ten  long- 
turn  elbows?    The  friction  head  is  not  to  exceed  10  ft.,  and  the 
velocity  of  flow  not  to  exceed  300  feet  per  minute.    ANS.  4-inch. 

3.  What  horse-power  will  be   required   to  drive  a  centrifugal 
pump  delivering  400  gallons  per  minute  against  a  friction  head  of 
40  feet,  assuming  an  efficiency  of  50  per  cent  for  the  pump? 

ANS.  8  H.  P. 


111.     Centrifugal    Pump  Direct -Con- 
nected to  Engine,  for  Forced  Hot- 
Water  Circulation. 


319 


124  HEATING  AND  VENTILATION 

4.  A  building  contains  10,000  square  feet  of  direct  radiation  and 
5,000*  square  feet  of  indirect  radiation.     Steam  at  atmospheric  pres- 
sure is  to  be  used.     The  initial  temperature  of  the  water  is  to  be  200°; 
and  the  final,  160°.     How  many  square  feet  of  heating  surface  should 
the  heater  contain?  Axs.  575  sq.  ft. 

5.  How   many  square   feet   would   be   required   in   the   above 
heater  (Example  4)  if  the  initial  temperature  of  the  water  were  180° 
and   the   final   temperature    150°?  Axs.  399  sq.  ft. 

EXHAUST=STEAM  HEATING 

Steam,  after  being  used  in  an  engine,  contains  the  greater  part 
of  its  heat ;  and  if  not  condensed  or  used  for  other  purposes,  it  can 
usually  be  employed  for  heating  without  affecting  to  any  great  extent 
the  power  of  the  engine.  In  general,  we  may  say  that  it  is  a  matter  of 
economy  to  use  the  exhaust  for  heating,  although  various  factors 
must  be  considered  in  each  case  to  determine  to  what  extent  this  is 
true.  The  more  important  considerations  bearing  upon  the  matter 
are:  the  relative  quantities  of  steam  required  for  power  and  for 
heating;  the  length  of  the  heating  seaso-n;  the  type  of  engine  used; 
the  pressure  carried;  and,  finally,  whether  the  plant  under  con- 
sideration is  entirely  new,  or  whether,  on  the  other  hand,  it  involves 
the  adapting  of  an  old  heating  system  to  a  new  plant. 

The  first  use  to  be  made  of  the  exhaust  steam  is  the  heating  of 
the  feed-water,  as  this  effects  a  constant  saving  both  summer  and 
winter,  and  can  be  done  without  materially  increasing  the  back- 
pressure on  the  engine.  Under  ordinary  conditions,  about  one-sixth 
of  the  steam  supplied  to  the  engine  can  be  used  in  this  way,  or  more 
nearly  one-fifth  of  the  exhaust  discharged  from  the  engine. 

"We  may  assume  in  average  practice  that  about  SO  per  cent  of 
the  steam  supplied  to  an  engine  is  discharged  in  the  form  of  steam 
at  a  lower  pressure,  the  remaining  20  per  cent  being  partly  converted- 
into  work  and  partly  lost  through  cylinder  condensation.  Taking 
this  into  account,  there  remains,  after  deducting  the  steam  used  for 
feed-water  heating,  .8  X  f  =  .64  of  the  entire  quantity  of  steam 
supplied  to  the  engine,  available  for  heating  purposes. 

^Tien  the  quantity  of  steam  required  for  heating  is  small  com- 
pared with  the  total  amount  supplied  to  the  engine,  or  where  the 
heating  season  is  short,  it  is  often  more  economical  to  run  the  engine 


HEATING  AND  VENTILATION  125 

condensing  and  use  the  live  steam  for  heating.  This  can  be  deter- 
mined in  any  particular  case  by  computing  the  saving  in  fuel  by  the 
use  of  a  condenser,  taking  into  account  the  interest  and  depreciation 
on  the  first  cost  of  the  condensing  apparatus,  and  the  cost  of  water, 
if  it  must  be  purchased,  and  comparing  it  with  the  cost  of  heating 
with  live  steam. 

Usually,  however,  in  the  case  of  office  buildings  and  institutions, 
and  commonly  in  the  case  of  shops  and  factories,  especially  in  north- 
erly latitudes,  it  is  advantageous  to  use  the  exhaust  for  heating,  even  if 
a  condenser  is  installed  for  summer  use  only.  The  principal  objec- 
tion raised  to  the  use  of  exhaust  steam  has  been  the  higher  back- 
pressure required  on  the  engines,  resulting  in  a  loss  of  power  nearly 
proportional  to  the  ratio  of  the  back-pressure  to  the  mean  effective 
pressure.  There  are  two  ways  of  offsetting  this  loss — one,  by  raising 
the  initial  or  boiler  pressure;  and  the  other,  by  increasing  the  cut- 
off of  the  engine.  Engines  are  usually  designed  to  work  most  econom- 
ically at  a  given  cut-off,  so  that  in  most  cases  it  is  undesirable  to 
change  it  to  any  extent.  Raising  the  boiler  pressure,  on  the  other 
hand,  is  not  so  objectionable  if  the  increase  amounts  to  only  a  few 
pounds. 

Under  ordinary  conditions  in  the  case  of  a  simple  engine,  a  rise 
of  3  pounds  in  the  back-pressure  calls  for  an  increase  of  about  5 
pounds  in  the  boiler  pressure,  to  maintain  the  same  power  at  the 
engine. 

The  indicator  card  shows  a  back-pressure  of  about  2  pounds 
when  an  engine  is  exhausting  into  the  atmosphere,  so  that,  an  increase 
of  3  pounds  would  bring  the  pressure  up  to  a  total  of  5  pounds  which 
should  be  more  than  sufficient  to  circulate  the  steam  through  any 
well-designed  heating  system. 

If  it  is  desired  to  reduce  rather  than  increase  the  back-pressure, 
one  of  the  so-called  vacuum  systems,  described  later,  can  be  used. 

The  systems  of  steam  heating  which  have  been  described  are 
those  in  which  the  water  of  condensation  flows  back  into  the  boiler 
by  gravity.  Where  exhaust  steam  is  used,  the  pressure  is  much  below 
that  of  the  boiler,  and  it  must  be  returned  either  by  a  pump  or  by  a 
return  trap.  The  exhaust  steam  is  often  insufficient  to  supply  the 
entire  heating  system,  and  must  be  supplemented  by  live  steam  taken 
directly  from  the  boiler.  This  must  first  pass  through  a  reducing 


321 


126  HEATING  AND  VENTILATION 

valve  in  order  to  reduce  the  .pressure  to  correspond  with  that  carried 
in  the  heating  system. 

An  engine  does  not  deliver  steam  continuously,  but  at  regular 
intervals,  at  the  end  of  each  stroke;  and  the  amount  is  likely  to  vary 
with  the  work  done,  since  the  governor  is  adjusted  to  admit  steam  in 
such  a  quantity  as  is  required  to  maintain  a  uniform  speed.  If  the 
work  is  light,  very  little  steam  will  be  admitted  to  the  engine;  and 
for  this  reason  the  supply  available  for  heating  may  vary  somewhat, 
depending  upon  the  use  made  of  the  power  delivered  by  the  engine. 
In  mills  the  amount  of  exhaust  steam  is  practically  constant;  in 
office  buildings  where  power  is  used  for  lighting,  the  variation  is 
greater,  especially  if  power  is  also  required  for  the  running  of  elevators. 

The  general  requirements  for  a  successful  system  of  exhaust 
steam  heating  include  a  system 'of  piping  of  such  proportions  that 
only  a  slight  increase  in  back-pressure  will  be  thrown  upon  the  engine; 
a  connection  which  shall  automatically  supply  live  steam  at  a  reduced 
pressure  as  needed;  provision  for  removing  the  oil  from  the  exhaust 
steam ;  a  relief  or  back-pressure  valve  arranged  to  prevent  any  sudden 
increase  in  back  pressure  on  the  engine;  and  a  return  system  of  some 
kind  for  returning  the  water  of  condensation  to  the  boiler  against 
a  higher  pressure.  These  requirements  may  be  met  in  various  ways, 
depending  upon  actual  conditions  found  in  different  cases. 

To  prevent  sudden  changes  in  the  back-pressure,  due  to  irregular 
supply  of  steam,  the  exhaust  pipe  from  the  engine  is  often  carried  to 
a  closed  tank  having  a  capacity  from  30  to  40  times  that  of  the  engine 
cylinder.  This  tank  may  be  provided  with  baffle-plates  or  other 
arrangements  and  may  serve  as  a  separator  for  removing  the  oil  from 
the  steam  as  it  passes  through. 

Any  system  of  piping  may  be  used;  but  great  care  should  be 
taken  that  as  little  resistance  as  possible  is  introduced  at  bends  and 
fittings ;  and  the  mains  and  branches  should  be  of  ample  size.  Usually 
the  best  results  are  obtained  from  the  system  in  which  the  main  steam 
pipe  is  carried  directly  to  the  top  of  the  building,  the  distributing  pipes 
being  run  from  that  point,  and  the  radiating  surfaces  supplied  by  a 
down-flowing  current  of  steam. 

Before  taking  up  the  matter  of  piping  in  detail  a  few  of  the  more 
important  pieces  of  apparatus  will  be  described  in  a  brief  way. 

Reducing  Valves.    The  action  of  pressure-reducing  valves  has 


HEATING  AND  VENTILATION  127 

been  taken  up  quite  fully  in  "Boiler  Accessories/'  and  need  not  be 
repeated  here.  When  the  reduction  in  pressure  is  large,  as  in  the 
case  of  a  combined  power  and  heating  plant,  the  valve  may  be  one  or 
two  sizes  smaller  than  the  low-pressure  main  into  which  it  discharges. 
For  example,  a  5-inch  valve  will  supply  an  8-inch  main,  a  4-inch  a 
6-inch  main,  a  3-inch  a  5-inch  main,  a  2^-inch  a  4-inch  main,  etc. 

For  the  smaller  sizes,  the  difference  should  not  be  more  than  one 
size.  All  reducing  valves  should  be  provided  with  a  valved  by-pass 
for  cutting  out  the  valve  in  case  of  repairs.  This  connection  is  usually 
made  as  shown  in  plan  by  Fig.  112. 

Grease  Extractor.  When  exhaust  steam  is  used  for  heating  pur- 
poses, it  must  first  be  passed  through  some  form  of  separator  for 
removing  the  oil ;  and  as  an  additional  precaution  it  is  well  to  pass  the 


BY-PASS 

Fig.  118.    Connections  of  Reducing  Valve  in  Exhaust-Steam  Heating  System. 

water  of  condensation  through  a  separating  tank  before  returning  it  to 
the  boilers. 

Such  an  arrangement  is  shown  in  Fig.  113.  As  the  oil  collects 
on  the  surface  of  the  water  in  the  tank,  it  can  be  made  to  overflow 
into  the  sewer  by  closing  the  valve  in  the  connection  with  the  receiving 
tank,  for  a  short  time. 

As  much  of  the  oil  as  possible  should  be  removed  before  the 
steam  enters  the  pipes  and  radiators,  else  a  coating  will  be  formed  on 
their  inner  surfaces,  which  will  reduce  their  heating  efficiency.  The 
separation  of  the  oil  is  usually  effected  by  introducing  a  series  of 
baffling  plates  in  the  path  of  the  steam;  the  particles  of  oil  striking 
these  are  stopped,  and  thus  separated  from  the  steam.  The  oil  drops 
into  a  receiver  provided  for  this  purpose  and  is  discharged  through  a 
trap  to  the  sewer. 

In  the  separator,  or  extractor,  shown  in  Fig.  114,  the  separation  is 
accomplished  by  a  series  of  plates  placed  in  a  vertical  position  in  the 


12S 


IIKATING  AND  VENTILATION 


body  of  the  separator,  through  which  the  steam  must  pass.  These 
plates  consist  of  upright  hollow  columns,  with  openings  at  regular 
intervals  for  the  admission  of  water  and  oil,  which  drain  downward 
to  the  receiver  below.  The  steam  takes  a  zigzag  course,  and  all  of 
it  comes  in  contact  with  the  intercepting  plates,  which  insures  a 
thorough  separation  of  the  oil  and  other  solid  matter  from  the  steam. 
Another  form,  shown  in  Fig.  11."),  gives  excellent  results,  and  has  the 
advantage  of  providing  an  equalizing  chamber  for  overcoming,  to 
some  extent,  the  unequal  pressure  due  to  the  varying  load  on  the 
engine.  It  consists  of  a  tank  or  receiver  about  4  feet  in  diameter, 
with  heavv  boiler-iron  heads  sli<rhtlv  crowned  to  mve  stiffness. 


Water-line  in 


Receiving  Tank  ,...£~ — -ji 'Oil  < 


foReceivi-ngTe 
4 


Oil  Over-Flovy 


S-u.rfa.cc 


Main  Ret-u-m 
From  Trap 


Fij.'.  113.    Separator  for  Removing  Oil  from  Exhaust  Steam  and  Water  Condensation. 

Through  the  center  is  a  layer  of  excelsior  (wooden  shavings  of  long 
fibre)  about  12  inches  in  thickness,  supported  on  an  iron  grating, 
with  a  similar  grating  laid  over  the  top  to  hold  it  in  place.  The 
steam  enters  the  space  below  the  excelsior  and  passes  upward,  as 
shown  by  the  arrows.  The  oil  is  caught  by  the  excelsior,  which  can 
be  renewed  from  time  to  time  as  it  becomes  saturated.  The  oil  and 
water  which  fall  to  the  bottom  of  the  receiver  are  carried  off  through 
a  trap.  Live  steam  may  be  admitted  through  a  reducing  valve,  for 
supplementing  the  exhaust  when  necessary. 

Backpressure  Valve.  This  is  a  form  of  relief  valve  which  is 
placed  in  the  outboard  exhaust  pipe  to  prevent  the  pressure  in  the 
heating  system  from  rising  above  a  given  point.  Its  office  is  the 


324 


HEATING  AND  VENTILATION 


129 


reverse  of  the  reducing  valve,  which  supplies  more  steam  when 
the  pressure  becomes  too  low.  The  form  shown  in  Fig.  116  is 
designed  for  a  vertical  pipe.  The  valve  proper  consists  of  two  discs 
of  unequal  area,  the  combined  area  of  which  equals  that  of  the  pipe. 
The  force  tending  to  open  the  valve  is  that  due  to  the  steam  pressure 
acting  on  an  area  equal  to  the  difference  in  area  between  the  two  discs ; 
it  is  clear  from  the  cut  that  the 
pressure  acting  on  the  larger 
disc  tends  to  open  the  valve 
while  the  pressure  on  the  smal- 
ler acts  in  the  opposite  direc- 
tion. The  valve-stem  is  con- 
nected by  a  link  and  crank 
arm  with  a  spindle  upon  which 
is  a  lever  and  weight  outside. 
As  the  valve  opens,  the  weight 
is  raised,  so  that,  by  placing  it 
in  different  positions  on  the 
lever  arm,  the  valve  will  open 
at  any  desired  pressure. 

Fig.  117  shows  a  different 
type,  in  which  a  spring  is  used 
instead  of  a  weight.  This 
valve  has  a  single  disc  moving  RECEIVER 
in  a  vertical  direction.  The 
valve  stem  is  in  the  form  of  a 
piston  or  dash-pot  which  pre- 
vents a  too  sudden  movement 
and  makes  it  more  quiet  in 
its  action.  The  disc  is  held 
on  its  seat  against  the  steam 
pressure  by  a  lever  attached 
to  the  spring  as  shown.  When 
the  pressure  of  the  steam  on  the  underside  becomes  greater  than  the 
tension  of  the  spring,  the  valve  lifts  and  allows  the  steam  to  escape. 
The  tension  of  the  spring  can  be  varied  by  means  of  the  adjusting 
screw  at  its  upper  end. 

A  back-pressure  valve  is  simply  a  low-pressure  safety-valve 


DISCHARGE 


Pig.  114.    Oil  Separator  Consisting  of  Vertical 

Plates  with  Openings  Giving  Steam  a 

Zigzag  Course. 


130 


HEATING  AND  VENTILATION 


designed  with  a  specially  large  opening  for  the  passage  of  steam 
through  it.  These  valves  are  made  for  horizontal  as  well  as  for 
vertical  pipes. 


LIVE    STEA 
FROM  REDUCING 
VALVE 


EXHAUST t 

FROM  ENC/NE 


EXCELS/OR  / 


\STEAM  TO 
HEATING 
SYSTEM 


\HANDHOLE 


( >il  Separ 


>r  Consisting  of  a  Tank  in  which  Steam  is  Filtered  by  Passing 
Upward  through  a  Layer  of  Excelsior. 


Exhaust  Head.  This  is  a  form  of  separator  placed  at  the  top 
of  an  outboard  exhaust  pipe  to  prevent  the  water  carried  up  in  the 
steam  from  falling  upon  the  roofs  of  buildings  or  in  the  street  below. 
Fig.  118  is  known  as  a  centrifugal  exhaust  head.  The  steam,  on 
entering  at  the  bottom,  is  given  a. 
whirling  or  rotary  motion  by  the 
spiral  deflectors;  and  the  water  is 
thrown  outward  by  centrifugal  force 
against  the  sides  of  the  chamber,  from 
which  it  flows  into  the  shallow  trough 
at  the  base,  and  is  carried  away  through 
the  drip-pipe,  which  is  brought  down 
and  connected  with  a  drain-pipe  in- 
side the  building.  The  passage  of  the 
steam  outboard  is  shown  by  the  arrows. 
Other  forms  are  used  in  which  the 
water  is  separated  from  the  steam  by 
deflectors  which  change  the  direction  of 
the  currents. 

Automatic  Return=Pumps.  In  exhaust  heating  plants,  the 
condensation  is  returned  to  the  boilers  by  means  of  some  form  of 
return-pump.  A  combined  pump  and  receiver  of  the  form  illus- 


Kig.  1 16.    Automatically  Acting  Back- 
pressure Valve  Attached  to  Ver- " 
tical   Pipe.      For   Preventing 
Rise  of  Pressure  in  System 
above   any   Desired 
Point. 


HEATING  AND  VENTILATION 


131 


trated  in  Fig.  119  is  generally  used.  This  consists  of  a  cast-iron  or 
wrought-iron  tank  mounted  on  a  base  in  connection  with  a  boiler 
feed-pump.  Inside  the  tank  is  a  ball-float  connected  by  means  of 
levers  with  a  valve  in  the  steam  pipe  which  is  connected  with  the 
pump  When  the  water-line  in  the  tank  rises  above  a  certain  level, 
the  float  is  raised  and  opens  the  steam  valve,  which  starts  the  pump. 
When  the  water  is  lowered  to  its  normal  level,  the  valve  closes  and 
the  pump  stops.  By  this  arrangement,  a  constant  water-line  is 
maintained  in  the  receiver,  and  the  pump  runs  only  as  needed  to  care 
for  the  condensation  as  it  returns  from  the  heating  system.  If  dry 
returns  are  used,  they  may  be  brought  together  and  connected  with 
the  top  of  the  receiver.  If  it  is  desired  to  seal  the  horizontal  runs,  as 


Pig.  117.    Back-Pressure  Valve  Automatic- 
ally Operated  by  a  Spring. 


Fig.  118.    Centrifugal  Exhaust  Head. 


is  usually  the  case,  the  receiver  may  be  raised  to  a  height  sufficient 
to  give  the  required  elevation  and  the  returns  connected  near  the 
bottom  below  the  water-line. 

A  balance-pipe,  so  called,  should  connect  the  heating  main  with 
the  top  of  the  tank,  for  equalizing  the  pressure;  otherwise  the  steam 
above  the  water  would  condense,  and  the  vacuum  thus  formed  would 
draw  all  the  water  into  the  tank,  leaving  the  returns  practically  empty 
and  thus  destroying  the  condition  sought.  Sometimes  an  inde- 
pendent regulator  or  pump  governor  is  used  in  place  of  a  receiver. 
One  type  is  shown  in  Fig.  120.  The  return  main  is  connected  at 


327 


132 


HEATING  AND  VENTILATION 


the  upper  opening,  and  the  pump  suction  at  the  lower.  A  float  inside 
the  chamber  operates  the  steam  valve  shown  at  the  top,  and  the  pump 
works  automatically  as  in  the  case  just  described. 

If  it  is  desired  to  raise  the  water-line,  the  regulator  may  be 
elevated  to  the  desired  height  and  connections  made  as  shown  in 
Fig.  121. 

Return  Traps.  The  principle  of  the  return  trap  has  been  de- 
scribed in  "Boiler  Accessories,"  but  its  practical  form  and  application 


Pig.  119.    Combined  Receiver  and  Automatic  Pump  for  Returning  Water  of 
Condensation  to  Boiler. 

will  be  taken  up  here.  The  type  shown  in  Fig.  122  has  all  its  working 
parts  outside  the  trap.  It  consists  of  a  cast-iron  bowl  pivoted  at  0  and 
II.  There  is  an  opening  through  0  connecting  with  the  inside  of 
the  bowl.  The  pipe  K  connects  through  C  with  an  interior  pipe 
opening  near  the  top  (see  Fig.  123).  The  pipe  D  connects  with  a 
receiver,  into  which  all  the  returns  are  brought.  A  is  a  check-valve 
allowing  water  to  pass  through  in  the  direction  shown  by  the  arrow. 
E  is  a  pipe  connecting  with  the  boiler  below  the  water-line.  B  is  a 


HEATING  AND  VENTILATION 


133 


check  opening  to\vard  the  boiler,  and  K,  a  pipe  connected  with  the 
steam  main  or  drum. 

The  action  of  the  trap  is  as  fol- 
lows :  As  the  bowl  fills  with  water  from 
the  receiver,  it  overbalances  the 
weighted  lever  and  drops  to  the  bot- 
tom of  the  ring.  This  opens  the  valve 
C,  and  admits  steam  at  boiler  pres- 
sure to  the  top  of  the  trap.  Being  at 
a  higher  level  the  water  flows  by  grav- 
ity into  the  boiler,  through  the  pipe  E. 
Water  and  steam  are  kept  from  passing 
out  through  D  by  the  check  A. 

\\Tien  the  trap   has   emptied   it-  VI9^SSS^JS^SSSM 

.  „      ,        ,     ,,  .  of  a  Receiver. 

self,  the  weight  of  the  ball  raises  it 

to  the  original  position,  which  movement  closes  the  valve  C  and  opens 
the  small  vent  F.  The  pressure  in  the  bowl  being  relieved,  water 
flows  in  from  the  receiver  through  D,  until  the  trap  is  filled,  when  the 


K3 


A  U  TO  MA  T/C      VA  L  VE 


TO     PUMP 


Fig.  121.    Pump  Regulator  Placed  at  Sufficient  Height  to  Raise  Water- Line  to 
Point  Desired. 

process  is  repeated.     In  order  to  work  satisfactorily,  the  trap  should 
be  placed  at  least  3  feet  above  the  water-level  in  the  boiler,  and  the 


329 


134 


HEATING  AND  VENTILATION 


pressure  in  the  returns  must  always  be  sufficient  to  raise  the  water 
from  the  receiver  to  the  trap  against  atmospheric  pressure,  which  is 
theoretically  about  1  pound  for  every  2  feet  in  height.  In  practice 
there  will  be  more  or  less  friction  to 
overcome,  and  suitable  adjustments  must 
be  made  for  each  particular  case. 

Fig.  124  shows  another  form  of  trap 
acting  upon  the  same  principle,  except 
that  in  this  case  the  steam  valve  is  oper- 
ated by  a  bucket  or  float  inside  the  trap. 
The  pipe  connections  are  practically  the 
same  as  with  the  trap  just  described. 

Return  traps   are    more    commonly 
used  in  smaller  plants  where  it  is  desired  Fig  ]23.  Return  Trap  w}th  Work. 
to  avoid  the  expense  and  care  of  a  pump. 

Damper=Regulators.  Every  heating  and  every  power  plant 
should  be  provided  with  automatic  means  for  closing  the  dampers 
when  the  steam  pressure  reaches  a  certain  point,  and  for  opening 
them  again  when  the  pressure  drops.  There  are  various  regulators 
designed  for  this  purpose,  a  simple  form  of  which  is  shown  in  Fig.  125. 

Steam  at  boiler  pres- 
sure is  admitted  beneath  a 
diaphragm  which  is  bal- 
anced by  a  weighted  lever. 
When  the  pressure  rises  to  a 
certain  point,  it  raises  the 
lever  slightly  and  opens  a 
valve  which  admits  water 
under  pressure  above  a  dia- 
phragm located  near  the 
smoke-pipe.  This  action 
forces  down  a  lever  con- 
nected by  chains  with  the 
•ii  Trap  damper,  and  closes  it. 
When  the  steam  pressure 
drops,  the  water-valve  is  closed,  and  the  different  parts  of  the 
apparatus  take  their  original  positions. 

Another  form  similar  in  principle  is  shown  in  Fig.  126.     In  this 


Fig.  123.    Showing  Interior  Detail  of  Retur 
of  Fig.  122. 


880 


HEATING  AND  VENTILATION 


135 


case  a  piston  is  operated  by  the  water-pressure,  instead  of  a  diaphragm. 
In  both  types  the  pressures  at  which  the  damper  shall  open  and  close 
are  regulated  by  suitable  adjustments  of  the  weights  upon  the  levers. 
Pipe  Connections.  The  method  of  making  the  pipe  connections 
in  any  particular  case  will  depend  upon  the  general  arrangement 
of  the  apparatus  and  the  various  conditions.  Fig.  127  illustrates 


s& 


Pig.  134.    Return  Trap  with  Steam  Valve  Operated  by  Bucket  or  Float  Inside. 

the  general  principles  to  be  followed,  and  by  suitable  changes  may  be 
used  as  a  guide  in  the  design  of  new  systems. 

Steam  first  passes  from  the  boilers  into  a  large  drum  or  header. 
From  this,  a  main,  provided  with  a  shut-off  valve,  is  taken  as  shown; 
one  branch  is  carried  to  the  engines,  while  another  is  connected  with 
the  heating  system  through  a  reducing  valve  having  a  by-pass  and 
cut-out  valves.  The  exhaust  from  the  engines  connects  with  the  large 
main  over  the  boilers  at  a  point  just  above  the  steam  drum.  The 


331 


130 


HEATING  AND  VENTILATION 


branch  at  the  right  is  carried  outboard  through  a  back-pressure 
valve  which  may  be  set  to  carry  any  desired  pressure  on  the  system. 
The  other  branch  at  the  left  passes  through  an  oil  separator  into  the 
heating  system.  The  connections  between  the  mains  and  radiators 
are  made  in  the  usual  way,  and  the  main  return  is  carried  back  to  the 
return  pump  near  the  floor.  A  false  water-line  or  seal  is  obtained  by 
elevating  the  pump  regulator  as  already  described.  An  equalizing 


Fig.   125 
D 


125.    Simple  Form  of  Automatic  Damper-Regulator.  Operated  by  Lever  Attached  to 
Diaphragm,  for  Closing  Dampers  when  Steam  Pressure  Reaches  a  Certain  Point. 


or  balance  pipe  connects  the  top  of  the  regulator  with  the  low-pressure 
heating  main,  and  high  pressure  is  supplied  to  the  pump  as  shown. 

A  sight-feed  lubricator  should  be  placed  in  this  pipe  above  the 
automatic  valve;  and  a  valved  by-pass  should  be  placed  around  the 
regulator,  for  running  the  pump  in  case  of  accident  or  repairs.  The 
oil  separator  should  be  drained  through  a  special  oil  trap  to  a  catch- 
basin  or  to  the  sewer;  and  the  steam  drum  or  any  other  low  points 


332 


HEATING  AND  VENTILATION 


137 


or  pockets  in  the  high-pressure  piping  should  be  dripped  to  the 
return  tank  through  suitable  traps. 

Means  should  be  provided  for  draining  all  parts  of  the  system 
to  the  sewer,  and  all  traps  and  special  apparatus  should  be  by-passed. 
The  return -pump  should  always  be  duplicated  in  a  plant  of  any  size, 
as  a  safeguard  against  accident;  and  the  two  pumps  should  be  run 
alternately,  to  make  sure  that  one  is  always  in  working  order. 


Fig.  136.    Automatic  Damper-Regulator  Operated  by  Piston  Actuated 
by  Water-Pressure. 


One  piece  of  apparatus  not  shown  in  Fig.  127  is  the  feed -water 
heater.  If  all  of  the  exhaust  steam  can  be  utilized  for  heating  pur- 
poses, this  is  not  necessary,  as  the  cold  water  for  feeding  the  boilers 
may  be  discharged  into  the  return  pipe  and  be  pumped  in  with  the 
condensation.  In  summertime,  however,  when  the  heating  plant  is 
not  in  use,  a  feed-water  heater  is  necessary,  as  a  large  amount  of  heat 


138 


HEATING  AND  VENTILATION 


HEATING  AND  VENTILATION  139 

which  would  otherwise  be  wasted  may  be  saved  in  this  way.  The 
connections  will  depend  somewhat  upon  the  form  of  heater  used: 
but  in  general  a  single  connection  with  the  heating  main  inside  the 
hack-pressure  valve  is  all  that  is  necessary.  The  condensation  from 
the  heater  should  be  trapped  to  the  sewer. 


335 


336 


HEATING  AND  VENTILATION 

PART  III 


VACUUM  SYSTEMS 

Low=Pressure  or  Vacuum  Systems.  In  the  systems  of  steam 
heating  which  have  been  described  up  to  this  point,  the  pressure 
carried  has  always  been  above  that  of  the  atmosphere,  and  the  action 
of  gravity  has  been  depended  upon  to  carry  the  water  of  condensation 
back  to  the  boiler  or  receiver;  the  air  in  the  radiators  has  been  forced 
out  through  air-valves  by  the  pressure  of  steam  back  of  it.  Methods 
will  now  be  taken  up  in  which  the  pressure  in  the  heating  system  is 
less  than  the  atmosphere,  and  where 
the  circulation  through  the  radiators  is 
produced  by  suction  rather  than  by 
pressure.  Systems  of  this  kind  have 
several  advantages  over  the  ordinary 
methods  of  circulation  under  pressure. 
First — no  back-pressure  is  produced 
at  the  engines  when  used  in  connection 
with  exhaust  steam;  but  rather  there 
will  be  a  reduction  of  pressure  due  to 
the  partial  vacuum  existing  in  the  radia- 
tors. Second  —  there  .is  a  complete 
removal  of  air  from  the  coils  and 
radiators,  so  that  all  portions  are 
steam-filled  and  available  for  heating 
purposes.  Third — there  is  complete  drainage  through  the  returns, 
especially  those  having  long  horizontal  runs;  and  there  is  absence  of 
water-hammer.  Fourth  —  smaller  return  pipes  may  be  used. 
The  two  older  systems  of  this  kind  in  common  use  are  known  as  the 
Webster  and  Paul  systems;  other  systems  of  recent  introduction  are 
described  in  the  Instruction 'Paper  on  Steam  and  Hot- Water  Fitting. 

Webster  System.  This  consists  primarily  of  an  automatic  outlet- 
valve  on  each  coil  and  radiator,  connected  with  some  form  of  suction 
apparatus  such  as  a  pump  or  ejector.  One  type  of  valve  used  is 


Pig.  128,    Air  Outlet-Valve  for  Radi- 
ator, Automatically  Operated  by 
Expansion  and  Contraction 
of  Vulcanite  Stem. 


837 


142 


HEATING  AND  VENTILATION 


Fig.    129.      Thermostat     At- 
tached to  Angle- Valve  with 
Top  Removed. 


shown  in  section  in  Fig.  128,  which 'replaces  the  usual  hand-valve  at 
the  return  end  of  the  radiator.  It  is  similar  in  construction  to  some 
of  the  air-valves  already  described,  consisting  of  a  rubber  or  vulcanite 
stem  closing  against  a  valve  opening  when 
made  to  expand  by  the  presence  of  steam. 
When  water  or  air  fills  the  valve,  the  stem 
contracts  and  allows  it  to  be  sucked  out 
as  shown  by  the  arrows.  A  perforated 
metal  strainer  surrounds  the  stem  or  ex- 
pansion piece,  to  prevent  dirt  and  sediment 
from  clogging  the  valve. 

Fig.  129  shows  the  valve — or  thermostat, 
as  it  is  called — attached  to  an  ordinary 
angle-valve  with  the  top  removed;  and  Fig. 
130  indicates  the  method  of  draining  the 
bottoms  of  risers  or  the  ends  of  mains. 

Fig.  131  shows  another  form  of  this 
valve,  called  a  water-seal  motor.  This  is 
used  under  practically  the  same  conditions 
as  the  one  described  above.  Its  action  is  as  follows : 

Ordinarily,  the  seal  .1  is  down,  and  the  central  tube-valve  is 
resting  upon  the  seat,  closing  the  port  K  and  preventing  direct  com- 
munication between  the  interior  of 
the  motor-body  E  and  the  outlet 
L.  The  outlet  is  attached  to  a  pipe 
leading  to  a  vacuum-pump,  or 
other  draining  apparatus,  which 
exhausts  the  space  F  above  the  seal 
through  the  annular  space  between 
the  spindle  B  and  the  inside  of  the 
central  tube  G.  The  water  of 
condensation,  accumulating  in  the 
radiator  or  coil,  passes  into  the 
chamber  E,  through  the  inlet  C,  rises  in  the  chamber,  and  seals  the 
space  between  the  seal-shell  A  and  the  sleeve  of  the  bonnet  D.  The 
differential  pressure  thus  created  causes  the  seal  .1  to  rise,  lifting  the 
end  of  the  central  tube  off  the  seat,  thus  opening  a  clear  passageway 
for  the  ejection  of  the  water  of  condensation. 


Fig.  13fl.     Showing  Method  of  Draining 

Bottoms  of  Risers  or  Ends 

of  Mains. 


HEATING  AND  VENTILATION 


143 


When  all  the  water  of  condensation  has  been  drawn  out  of  the 
radiator,  the  seal  and  tube  are  reseated  by  gravity,  thus  closing  the 
port  K,  preventing  waste  or  loss  of  steam;  and  the  pressure  is  equal- 
ized above  and  below  the  seal  because  of  the  absence  of  water.  This 
action,  is  practically  instantaneous.  When  the  condensation  is  small 
in  quantity,  the  discharge  is  intermittent  and  rapid. 

The  space  between  the  seal  A  and  the  sleeve  of  the  bonnet  D, 
and  the  annular  space  between  the  central  tube  G  and  the  spindle  B, 


Fig.  131.    Water-Seal  Motor. 

form  a  passageway  through  which  the  air  is  continually  withdrawn  by 
the  vacuum  pump  or  other  draining  apparatus. 

The  action  outlined  continues  as  long  as  water  is  present. 

No  adjustment  whatever  is  necessary;  the  motor  is  entirely  auto- 
matic. 

One  special  advantage  claimed  for  this  system  is  that  the  amount 
of  steam  admitted  to  the  radiators  may  be  regulated  to  suit  the  require- 
ments of  outside  temperature;  and  is  possible  without  water- 


144 


HEATING  AND  VENTILATION 


340 


HEATING  AND  VENTILATION  145 

logging  or  hammering.  This  may  be  done  at  will  by  closing  down  on 
the  inlet  supply  to  the  desired  degree.  The  result  is  the  admission 
of  a  smaller  amount  of  steam  to  the  radiator  than  it  is  calculated  to 
condense  normally.  The  condensation  is  removed  as  fast  as  formed, 
by  the  opening  of  the  thermostatic  valve. 

The  general  application  of  this'  system  to  exhaust  heating  is 
shown  in  Fig.  132.  Exhaust  steam  is  brought  from  the  engine  as 
shown;  one  branch  is  connected  with  a  feed-water  heater,,  while  the 
other  is  carried  upward  and  through  a  grease  extractor,  where  it 
branches  again,  one  line  leading  outboard  through  a  back-pressure 
valve  and  the  other  connecting  with  the  heating  main.  A  live  steam 
connection  is  made  through  a  reducing  valve,  as  in  the  'ordinary 
system.  Valved  connections  are  made  with  the  coils  and  radiators 
in  the  usual  manner;  but  the  return  valves  are  replaced  by  the  special 
thermostatic  valves  described  above. 

The  main  return  is  brought  down  to  a  vacuum  pump  which  dis- 
charges into  a  return  tank,  where  the  air  is  separated  from  the  water 
and  passes  off  through  the  vapor  pipe  at  the  top.  The  condensation 
then  flows  into  the  feed-water  heater,  from  which  it  is  automatically 
pumped  back  into  the  boilers.  The  cold-water  feed  supply  is  con- 
nected with  the  return  tank,  and  a  small  cold-water  jet  is  connected 
into  the  suction  at  the  vacuum  pump  for  increasing  the  vacuum  in -the 
heating  system  by  the  condensation  of  steam  at  this  point. 

Paul  System.  In  this  system  the  suction  is  connected  with  the 
air-valves  instead  of  the  returns,  and  the  vacuum  is  produced  by 
means  of  a  steam  ejector  instead  of  a  pump.  The  returns  are  carried 
back  to  a  receiving  tank,  and  pumped  back  to  the  boiler  in  the  usual 
manner.  The  ejector  in  this  case  is  called  the  exhauster. 

Fig.  133  shows  the  general  method  of  making  the  pipe  connections 
with  the  radiators  in  this  system;  and  Fig.  134,  the  details  of  connec- 
tion at  the  exhauster. 

A  A  are  the  returns  from  the  air-valves,  and  connect  with  the 
exhausters  as  shown.  Live  steam  is  admitted  in  small  quantities 
through  the  valves  B  B ;  and  the  mixture  of  air  and  steam  is  discharged 
outboard  through  the  pipe  C.  D  D  are  gauges  showing  the  pressure 
in  the  system;  and  E  E  are  check-valves.  The  advantage  of  this 
system  depends  principally  upon  the  quick  removal  of  air.  from  the 
various  radiators  and  pipes,  which  constitutes  the  principal  obstruction 


341 


I4r> 


HEATING  AND  VENTILATION 


to  circulation;  the  inductive  action  in  many  cases  is  sufficient  to  cause 
the  system  to  operate  somewhat  below  atmospheric  pressure. 

Where  exhaust  steam  is  used  for  heating,  the  radiators  should 


fMVi     SYSTEM  OF  HCATIN* 


Fit:.  133.     Showing  General  Method  Of  Making  Pipe  and  Radiator  Connections  in 
Paul  System. 


be  somewhat  increased  in  size,  owing  to  the  lower  temperature  of 
the  steam.  It  is  common  practice  to  add  from  20  to  30  per  cent  to 
the  sizes  required  for  low-pressure  live  steam. 


HEATING  AND  VENTILATION 


147 


FORCED  BLAST 

In  a  system  of  forced  circulation  by  means  of  a  fan  or  blower 
the  action  is  positive  and  practically  constant  under  all  usual  con- 
ditions of  outside  temperature  and  wind  action.     This  gives  it  a 
decided  advantage  over  natural  or  gravity  methods,  which  are  af- 
A  A 


B  B 

Fig.  134.    Details  of  Connections  at  Exhauster,  Paul  System. 

fected  to  a  greater  or  less  degree  by  changes  in  wind-pressure,  and 
makes  it  especially  adapted  to  the  ventilation  and  warming  of  large 
buildings  such  as  shops,  factories,  schools,  churches,  halls,  theaters, 
etc.,  where  large  and  definite  air-quantities  are  required. 

Exhaust   Method.    This  consists  in  drawing  the  air  out  of  a 
building,  and  providing  for  the  heat  thus  carried  away  by  placing 


343 


148  HEATING  AND  VENTILATION 


steam  coils  under  windows  or  in  other  positions  where  the  inward 
leakage  is  supposed  to  be  the  greatest.  When  this  method  is  used,  a 
partial  vacuum  is  created  within  the  building  or  room,  and  all  currents 
and  leaks  are  inward ;  there  is  nothing  to  govern  definitely  the  quality 
and  place  of  introduction  of  the  air,  and  it  is  difficult  to  provide  suit- 
able means  for  warming  it. 

Plenum  Method.  In  this  case  the  air  is  forced  into  the  building, 
and  its  quality,  temperature,  and  point  of  admission  are  completely 
under  control.  All  spaces  are  filled  with  air  under  a  slight  pressure, 
and  the  leakage  is  outward,  thus  preventing  the  drawing  of  foul  air 
into  the  room  from  any  outside  source.  But  above  all,  ample  oppor- 
tunity is  given  for  properly  warming  the  air  by  means  of  heaters, 
either  in  direct  connection  with  the  fan  or  in  separate  passages  leading 
to  the  various  rooms. 

Form  of  Heating  Surface.  The  best  type  of  heater  for  any 
particular  case  will  depend  upon  the  volume  and  final  temperature 
of  the  air,  the  steam  pressure,  and  the  available  space.  When  the 
air  is  to  be  heated  to  a  high  temperature  for  both  warming  and  venti- 
lating a  building,  as  in  the  case  of  a  shop  or  mill,  heaters  of  the  general 
form  shown  in  Figs.  135,  136,  and  137  are  used.  These  may  also  be 
adapted  to  all  classes  of  work  by  varying  the  proportions  as  required. 
They  can  be  made  shallow  and  of  large  superficial  area,  for  the  com- 
paratively low  temperatures  used  in  purely  ventilating  work;  or 
deeper,  with  less  height  and  breadth,  as  higher  temperatures  are 
required. 

Fig.  135  shows  in  section  a  heater  of  this  type,  and  illustrates 
the  circulation  of  steam  through  it.  It  consists  of  sectional  cast-iron 
bases  with  loops  of  wrought-iron  pipe  connected  as  shown.  The 
steam  enters  the  upper  part  of  the  bases  or  headers,  and  passes  up 
one  side  of  the  loops,  then  across  the  top  and  down  on  the  other  side, 
where  the  condensation  is  taken  off  through  the  return  drip,  which 
is  separated  from  the  inlet  by  a  partition.  These  heaters  are  made 
up  in  sections  of  2  and  4  rows  of  pipes  each.  The  height  varies  from 
3^  to  9  feet,  and  the  vidth  from  3  feet  to  7  feet  in  the  standard  sizes. 
They  are  usually  made  up  of  1-inch  pipe,  although  l|-inch  is  commonly 
used  in  the  larger  sixes.  Fig.  136  shows  another  form;  in  this  case 
all  the  loops  are  made  of  practically  the  same  length  by  the  special 
form  of  construction  shown.  This  is  claimed  to  prevent  the  short- 


344 


HEATING  AND  VENTILATION 


149 


circuiting  of  steam  through  the  shorter  loops,  which  causes  the  outer 
pipes  to  remain  gold.     This  form  of  heater  is  usually  encased  in  a 


Fig.  135.    Showing  Circulation  of  Steam  in  Large  Coil-Pipe  Radiator  for 
Heating  Mills,  Shops,  etc. 

sheet-steel  housing  as  shown  in  Fig.  137,  but  may  be  supported  on 
foundation  between  brick  walls  if  desired. 


845 


150 


HEATING  AND  VENTILATION 


Fig.  138  shows  a  special  form  of  heater  particularly  adapted  to 
ventilating  work  where  the  air  does  not  have  to  he  raised  above  70  or 
SO  degrees.  It  is  made  up  of  1-inch  wrought-iron  pipe  connected 


with  supply  and  return  headers;  each  section  contains  14  pipes,  and 
they  are  usually  made  up  in  groups  of  5  sections  each.  These  coils 
are  supported  upon  tee-irons  resting  upon  a  brick  foundation.  Heat- 


346 


HEATING  AND  VENTILATION 


151 


ers  of  this  form  are  usually  made  to  extend  across  the  side  of  a  room 
with  brick  walls  at  the  sides,  instead  of  being  encased  in  steel  housings. 

Fig.  139  shows  a  front  view  of  a  cast-iron  sectional  heater  for 
use  under  the  same  conditions  as  the  pipe  heaters  already  described. 
This  heater  is  made  up  of  several  banks  of  sections,  like  the  one  shown 
in  the  cut,  and  enclosed  in  a  steel-plate  casing. 

Cast-iron  indirect  radiators  of  the  pin  type  are  well  adapted  for 
use  in  connection  with  mechanical  ventilation,  and  also  for  heating 


Fig.  137.    Large  Coil-Pipe  Radiator  Encased  in  Sheet-Steel  Housing. 

where  the  air- volume  is  large  and  the  temperature  not  too  high,  as 
in  churches  and  halls.  They  make  a  convenient  form  of  heater,  for 
schoolhouse  and  similar  work,  for,  being  shallow,  they  can  be  sup- 
ported upon  I-beams  at  such  an  elevation  that  the  condensation  will  be 
returned  to  the  boilers  by  gravity. 

In  the  case  of  vertical  pipe  heaters,  the  bases  are  below  the  water- 
line  of  the  boilers,  and  the  condensation  must  be  returned  by  the  use 
of  pumps  and  traps. 


347 


152 


HEATING  AND  VENTILATION 


Efficiency  of  Pipe  Heaters.  The  efficiency  of  the  heaters  used  in 
connection  with  forced  blast  varies  greatly,  depending  upon  the 
temperature  of  the  entering  air,  its  velocity  between  the  pipes,  the 
temperature  to  which  it  is  raised,  and  the  steam  pressure  carried  in 
the  heater.  The  general  method  in  which  the  heater  is  made  up  is 
also  an  important  factor. 

In  designing  a  heater  of  this  kind,  care  must  be  taken  that  the 
free  area  between  the  pipes  is  not  contracted  to  such  an  extent  that 
an  excessive  velocity  will  be  required  to  pass  the  given  quantity  of 


GAL.  /RON  STOP 


PLAN  AT  SUPPLY  END 


FRONT  V/EW 
1I!S.     Heater  Especially  Adapted 


S/DE      V/EW 


o  Ventilation  where  Air  does  not  Have  to  be  Heated 
70  to  80  decrees  F. 


air  through  it.  In  ordinary  work  it  is  customary  to  assume  a  velocity 
of  800  to  1 ,000  feet  per  minute ;  higher  velocities  call  for  a  greater 
pressure  on  the  far.,  which  is  not  desirable  in  ventilating  work. 

In  the  heaters  shown,  about  .4  of  the  total  area  is  free  for  the 
passage  of  air;  that  is,  a  heater  5  feet  wide  and  6  feet  high  would 
have  a  total  area  of  5  X  6  =  30  square  feet,  and  a  free  area  between 
the  pipes  of  30  X  .  4  =  12  square  feet.  The  depth  or  number  of  rows 
of  pipe  does  not  affect  the  free  area,  although  the  friction  is  increased 
and  additional  work  is  thrown  upon  the  fan.  The  efficiency  in  any 


848 


HEATING  AND  VENTILATION 


153 


I 


given  heater  will  be  increased  by  increasing  the  velocity  of  the  air 
through  it;  but  the  final  temperature  will  be  diminished;  that  is, 
a  larger  quantity  of  air  will  be  heated  to  a  lower  temperature  in  the 
second  case,  and,  while  the  total  heat  given  off  is  greater,  the  air- 
quantity  increases  more  rapidly  than  the  heat-quantity,  which  causes 
a  drop  in  temperature. 

Increasing  the  number  of  rows  of  pipe  in  a  heater,  with  a  con- 
stant air-quantity,  increases  the  final  temperature  of  the  air,  but 
diminishes  the  efficiency  of  the  heater,  because  the  average  difference 
in  temperature  between  the  air  and  the  steam  is  less.  Increasing 
the  steam  pressure  in  the 
heater  (and  consequently  its 
temperature)  increases  both 
the  final  temperature  of  the 
air  and  the  efficiency  of  the 
heater.  Table  XXX  has  been 
prepared  from  different  tests, 
and  may  be  used  as  a  guide 
in  computing  probable  results 
under  ordinary  working  con- 
ditions. In  this  table  it  is 
assumed  that  the  air  enters 
the  heater  at  a  temperature  of 
zero  and  passes  between  the 
pipes  with  a  velocity  of  800 
feet  per  minute.  Column  1 
gives  the  number  of  rows  of 
pipe  in  the  heater,  ranging 
from  4  to  20  rows;  and  columns  2,  3,  and  4,  show  the  final  tempera- 
ture to  which  the  entering  air  will  be  raised  from  zero  under  various 
pressures.  Under  5  pounds  pressure,  for  example,  the  rise  in  tem- 
perature ranges  from  30  to  140  degrees;  under  20  pounds,  35  to  150 
degrees;  and  under  60  pounds,  45  to  170  degrees.  Columns  5, 6,  and 
7  give  approximately  the  corresponding  efficiency  of  the  heater.  For 
example,  air  passing  through  a  heater  10  pipes  deep  and  carrying  20 
pounds  pressure,  will  be  raised  to  a  temperature  of  90  degrees,  and 
the  heater  will  have  an  efficiency  of  1,650  B.  T.  U.  per  square  foot  of 
surface  per  hour. 


139.    Front  View  of  Cast-Iron  Sectional 
eater.    The  Banks  of  Sections  are  En- 
closed in  a  Steel-Plate  Casing. 


154 


HEATING  AND  VENTILATION 


TABLE  XXX 
Data  Concerning  Pipe  Heaters 

Temperature  of  entering  air,  zero. — Velocity  of  air  between  the  pipes, 
800  feet  per  minute. 


TEMPERATURE  TO  WHICH  AIR  WILL  EFFICIENCY  OF  HEATING  SURFACE  iN-B.T.U 
BE  RAISED  FROM  ZERO  PER  SQUARE  FOOT  PER  HOUR 


Rows  OF 
PIPK  DEEP         Steam  Pressure  in  Heater 


Steam  Pressure  in  Heater 


5  Ibs.   !  20  Ibs. 

60  Ibs. 

5  Ibs. 

2 

o  Ibs. 

e 

0  Ibs. 

4       30       35 

45 

1,600 

1,800 

f 

>,000 

6       50      55 

65 

1,600 

1,800 

c 

>,000 

8       65      70 

85 

1,500 

,650 

,850 

10       80      90 

105 

1,500 

,650 

,850 

12       95     105 

125 

,500 

,650 

,850 

14      105     120 

140 

,400 

,500 

,700 

16      120     130 

150 

,400 

,500 

,700 

18      130     140 

160 

,300 

.400 

,600 

20      140     150 

170 

,300 

,400 

,600 

For  a  velocity  of  1,000  feet,  multiply  the  temperatures  given  in 
the  table  by  .  9,  and  the  efficiencies  by  1.1. 

Example.  How  many  square  feet  of  radiation  will  be  required  to  raise 
600,000  cubic  feet  of  air  per  hour  from  zero  to  80  degrees,  with  a  velocity 
through  the  heater  of '800  feet  per  minute  and  a  steam  pressure  of  5  pounds? 
What  must  be  the  total  area  of  the  heater  front,  and  how  man}-  rows  of 
pipes  must  it  have? 

Referring  back  to  the  formula  for  heat  required  for  ventilation, 
we  have 

000,000  X  80  __ 

=  8/2,/2/  B.  T.  I  .  required. 
55 

Referring  to  Table  XXX,  we  find  that  for  the  above  conditions  a 
heater  10  pipes  deep  is  required,  and  that  an  efficiency  of  1,500 

B.  T.  U.  will    be  obtained.     Then       — ' —    =    582  square  feet  of 

1  ,oOO 

surface  required,  which  may   be   taken  as  600  in    round  numbers. 

600,000  .  :  10,000 

=  10,000  cubic  feet  ot  air  per  minute:  and  -  =  12. o 

GO  800 

square  feet  of  free  area  required  through  the  heater.     If  we  assume 
.4  of  the   total  heater  front  to  be  free  for  the  passage  of  air,  then 

12  5 

=  31  square  feet,  the  total  area  required. 


350 


HEATING  AND  VENTILATION 


155 


For  convenience  in  estimating  the  approximate  dimensions  of 
a  heater,  Table  XXXI  is  given.  The  standard  heaters  made  by  dif- 
ferent manufacturers  vary  somewhat,  but  the  dimensions  given  in 
the  table  represent  average  practice.  Column  3  gives  the  square 
feet  of  heating  surface  in  a  single  row  of  pipes  of  the  dimensions  given 
in  columns  1  and  2;  and  column  4  gives  the  free  area  between  the 
pipes. 

TABLE    XXXI 
Dimensions  of  Heaters 


WIDTH  OF  SECTION            HEIGHT  OF  PIPES 

SQUARE  FEET  OF 
SURFACE 

FREE  AHEA  THROUGH 
HEATER  IN  SQ.  FT. 

3  feet 

3  feet 

6  inches 

20 

4.2 

3    " 

4     " 

0       " 

22 

4.8 

3    " 

4     " 

6       " 

25 

5.4 

3    " 

5     " 

0       " 

28 

6.0 

4    " 

4     " 

6       " 

34 

7.2 

4    '" 

5     " 

0 

38 

8.0 

4    " 

5     " 

6 

42 

8.8 

4    " 

6     " 

0      " 

45 

9.6 

5    " 

5     " 

6       " 

52 

11.0 

5    " 

6     " 

0       " 

57 

12.0 

5    " 

6     " 

6       " 

62 

13.0 

5    " 

7     " 

0       " 

67 

14.0 

6    " 

6     " 

6       " 

75 

15.6 

6    " 

7     " 

0       " 

81 

16.8 

6    " 

7     " 

6 

87 

18.0 

6    " 

8     " 

0 

92 

19.2 

7    " 

7     " 

6       ': 

98 

21.0 

7    " 

8     " 

0       " 

108 

22.4 

7    " 

8     " 

6 

109 

23.8 

7    " 

9     " 

0       " 

116 

25.2 

In  calculating  the  total  height  of  the  heater,  add  1  foot  for  the 
base. 

These  sections  are  made  up  of  1-inch  pipe,  except  the  last  or 
7-foot  sections,  which  are  made  of  l|-inch  pipe. 

Using  this  table  in  connection  with  the  example 'just  given,  we 
should  look  in  the  last  column  for  a  section  having  a  free  area  of  12.5 
square  feet;  here  we  find  that  a  5  feet  by  6  feet  6  inches  section  has  a 
free  opening  of  13  square  feet  and  a  radiating  surface  of  62  square 


351 


156  HEATING  AND  VENTILATION 

feet.  The  conditions  call  for  10  rows  of  pipes  and  10  X  62  =  620 
square  feet  of  radiating  surface,  which  is  slightly  more  than  called  for, 
but  which  would  be  near  enough  for  all  practical  purposes. 

EXAMPLE  FOR  PRACTICE 

Compute  the  dimensions  of  a  heater  to  warm  20,000  cubic  feet 
of  air  per  minute  from  10  below  zero  to  70  degrees  above,  with  5 
pounds  steam  pressure. 

Axs.    1,164  sq.  ft.  of  rad.  surface  10  pipes  deep. 
25  scj.  ft.  free  area  through  heater. 

Use  twenty  5  ft.  by  6  ft.  sections,  side  by  side,  which  gives  24 
square  feet  area  and  1,140  square  feet  of  surface. 

The  general  method  of  computing  the  size  of  heater  for  any  given 
building  is  the  same  as  in  the  case  of  indirect  heating.  First  obtain 
the  B.  T.  U.  required  for  ventilation,  and  to  that  add  the  heat  loss 
through  walls,  etc.;  and  divide  the  result  by  the  efficiency  of  the 
heater  under  the  given  conditions. 

Example.  An  audience  hall  is  to  be  provided  with  400,000  cubic  feet 
of  air  per  hour.  The  heat  loss  through  \vaHs,  etc..  is  250,000  B.T.U.  per 
hour  in  zero  weather.  What  will  be  the  size  of  heater,  and  how  many  rows 
of  pipe  deep  must  it  be,  with  20  pounds  steam  pressure?' 

400,000  X  70 


o 


Therefore  250,000  +  509,090  -  759,090  B.  T.  U.,  total  to  be  supplied. 

We  must  next  find  to  what  temperature  the  entering  air  must 
be  raised  in  order  to  bring  in  the  required  amount  of  heat,  so  that  the 
number  of  rows  of  pipe  in  the  heater  may  be  obtained  and  its  corre- 
sponding efficiency  determined.  We  have  entering  the  room  for  pur- 
poses of  ventilation,  400,000  cubic  feet  of  air  every  hour,  at  a  tempera- 
ture of  70  degrees;  and  the  problem  now  becomes:  To  what  tem- 
perature must  this  air  be  raised  to  carry  in  250,000  B.  T.  U.  additional 
for  warming? 

We  have  learned  that  1  B.  T.  U.  will  raise  55  cubic  feet  of  air 
1  degree.  Then  250,000  B.  T.  U.  will  raise  250,000  X  55  cubic 
feet  of  air  1  degree. 

J>50,000j><j>5  =          , 

^00,000^ 
The  air  in  this  case  must  be  raised  to  70  +  34  =  104  degrees,  to  provide 


352 


HEATING  AND  VENTILATION  157 

for  both  ventilation  and  warming.     Referring  to  Table  XXX,  we  find 
that  a  heater  12  pipes  deep  will  be  required,  and  that  the  corre- 


sponding efficiency  of  the  heater  will  be  1  ,650  B.  T.  U.     Then 

1,650 

=  460  square  feet  of  surface  required. 

Efficiency  of  Cast=Iron  Heaters.  Heaters  made  up  of  indirect 
pin  radiators  of  the  usual  depth,  have  an  efficiency  of  at  least  1,500 
B.  T.  U.,  with  steam  at  10  pounds  pressure,  and  are  easily  capable  of 
warming  air  from  zero  to  80  degrees  or  over  when  computed  on  this 
basis.  The  free  space  between  the  sections  bears  such  a  relation  to 
the  heating  surface  that  ample  area  is  provided  for  the  flow  of  air 
through  the  heater,  without  producing  an  excessive  velocity. 

The  heater  shown  in  Fig.  139  may  be  counted  on  for  an  effi- 
ciency at  least  equal  to  that  of  a  pipe  heater;  and  in  computing  the 
depth,  one  row  of  sections  may  be  taken  as  representing  4  rows  of 
pipe. 

Pipe  Connections.  In  the  heater  shown  in  Fig.  135,  all  the 
sections  take  their  supply  from  a  common  header,  the  supply  pipe 
connecting  with  the  top,  and  the  return  being  taken  from  the  lower 
division  at  the  end,  as  shown. 

In  Fig.  137  the  base  is  divided  into  two  parts,  one  for  live  steam, 
and  the  other  for  exhaust.  The  supply  pipes  connect  with  the  upper 
compartments,  and  the  drips  are  taken  off  as  shown.  Separate  traps 
should  be  provided  for  the  two  pressures. 

The  connections  in  Fig.  136  are  similar  to  those  just  described, 
except  that  the  supply  and  return  headers,  or  bases,  are  drained 
through  separate  pipes  and  traps,  there  being  a  slight  difference  in 
pressure  between  the  two,  which  is  likely  to  interfere  with  the  proper 
drainage  if  brought  into  the  same  one.  This  heater  is  arranged  to 
take  exhaust  steam,  but  has  a  connection  for  feeding  in  live  steam 
through  a  reducing  valve  if  desired,  the  whole  heater  being  under  one 
pressure. 

In  heating  and  ventilating  work  where  a  close  regulation  of 
temperature  is  required,  it  is  usual  to  divide  the  heater  into  several 
sections,  depending  upon  its  size,  and  to  provide  each  with  a  valve  in  the 
supply  and  return.  In  making  the  divisions,  special  care  should  be 
taken  to  arrange  for  as  many  combinations  as  possible.  For  example, 
a  heater  10  pipes  deep  may  be  made  up  of  three  sections  —  one  of 


353 


158 


HEATING  AND  VENTILATION 


2  rows,  and  two  of  4  rows  each.  By  means  of  this  division,  2,  4,  6,  8, 
or  10  rows. of  pipe  can  be  used  at  one  time,  as  the  outside  weather 
conditions  may  require. 

When  possible,  the  return  from  each  section  should  be  provided 
with  a  water-seal  two  or  three  feet  in  depth.  In  the  case  of  overhead 
heaters,  the  returns  may  be  sealed  by  the  water-line  of  the  boiler  or 
by  the  use  of  a  special  water-line  trap;  but  vertical  pipe  heaters 
resting  on  foundations  near  the  floor  are  usually  provided  with  siphon 
loops  extending  into  a  pit.  If  this  arrangement  is  not  convenient,  a 
separate  trap  should  be  placed  on  the  return  from  each  section. 
The  main  return,  in  addition  to  its  connection  with  the  boiler  or 


L/VE    STEAM 


EXHAUST  STEAM 


TRAP  TRAP 

Fig.  140.    Heater  Made  Up  of  Interchangeable  Sections. 


pump  receiver,  should  have  a  connection  with  the  sewer  for  blowing 
out  when  steam  is  first  turned  on.  Sometimes  each  section  is  pro- 
vided with  a  connection  of  this  kind. 

Large  automatic  air-valves  should  be  connected  with  each 
section;  and  it  is  well  to  supplement  these  with  a  hand  pet-cock, 
unless  individual  blow-off  valves  are  provided  as  described  above. 

If  the  fan  is  driven  by  a  steam  engine,  provision  should  be  made 
for  using  the  exhaust  in  the  heater;  and  part  of  the  sections  should 
be  so  valved  that  they  may  be  supplied  with  either  exhaust  or  live 
steam. 


354 


HEATING  AND  VENTILATION 


159 


Fig.  140  shows  an  arrangement  in  which  all  of  the  sections  are 
interchangeable. 

From  50  to  60  square  feet  of  sadiating  surface  should  be  provided 
in  the  exhaust  portion  of  the  heater  for  each  engine  horse-power, 
and  should  be  divided  into  at  least  three  sections,  so  that  it  can  be 
proportioned  to  the  requirements  of  different  outside  temperatures. 

Pipe  Sizes.  The  sizes  of  the  mains  and  branches  may  be  com- 
puted from  the  tables  already  given  in  Part  II,  taking  into  account 
the  higher  efficiency  of  the  heater  and  the  short  runs  of  piping. 

Table  XXXII,  based  on  experience,  has  been  found  to  give 
satisfactory  results  when  the  apparatus  is  near  the  boilers.  If  the 
main  supply  pipe  is  of  considerable  length,  its  diameter  should  be 
checked  by  the  method  previously  given. 

TABLE     XXXII 
Pipe  Sizes 


SQUARE  FEET  OF  SURFACE 

DIAMETER  OF  STEAM  PIPE 

DIAMETER  OF  RETURN 

150 

2     inches 

l\  inches 

300 

2* 

1*        " 

500 

3 

2 

700 

8J 

2         " 

1,000 
2,000 

4 
5 

II    " 

3,000 

6 

3        " 

Heaters  of  the  patterns  shown  in  Figs.  135,  136,  and  137  are 
usually  tapped  at  the  factory  for  high  or  low  pressure  as  desired, 
and  these  sizes  may  be  followed  in  making  the  pipe  connections. 

The  sizes  marked  on  Fig.  136  may  be  used  for  all  ordinary  work 
where  the  pressure  runs  from  5  to  20  pounds;  for  pressures  above 
that,  the  supply  connections  may  be  reduced  one  size. 

FANS 

There  are  two  types  of  fans  in  common  use,  known  as  the  cen- 
trifugal fan  or  blower,  and  the  disc  fan  or  propeller.  The  former 
consists  of  a  number  of  straight  or  slightly  curved  blades  extending 
radially  from  an  axis,  as  shown  in  Fig.  141.  When  the  fan  is  in 
motion,  the  air  in  contact  with  the  blades  is  thrown  outward  by  the 
action  of  centrifugal  force,  and  delivered  at  the  circumference  or 


355 


160 


HEATING  AND  VENTILATION 


periphery  of  the  wheel.     A  partial  vacuum  is  thus  produced  at  the 

center   of   the   wheel,  and   air  from  the  outside  flows  in  to  take  the 

place  of  that  which  has  been  discharged. 

Fig.  142  illustrates  the  action  of  a  centrifugal  fan,  the  arrows 

showing  the  path  of  the  air. 

This  type  of  fan  is  usually 

enclosed    in    a    steel  -  plate 

casing  of  such  form  as   to 

provide  for  the  free  move- 
ment of  the  air  as  it  es- 
capes from  the  periphery 

of  the  wheel.      An  opening 

in  the  circumference  of  the 

casing    serves    as  an  outlet 

into  the  distributing  ducts 

which  carry  the   air  to  the 

various  rooms  to  be  venti- 
lated. 

A  fan   with  casing,   is 

shown  in  Fig.   143;  and  a 

combined   heater   and   fan, 

with  direct-connected  engine,  is  shown  in  Fig.  144. 

The  discharge  opening  can  be  located  in  any  position  desired, 

either  up,  down,  top  horizontal,  bottom  horizontal,  o"  at  any  angle. 

Where  the  height  of  the  fan  room  is 
limited,  a  form  called  the  ihrcc-qnarlcr 
hominy  may  be  used,  in  which  the  lower 
part  of  the  casing  is  replaced  by  a  brick 
or  cemented  pit  extending  below  the  floor- 
level  as  shown  in  Fig.  145. 

Another  form  of  centrifugal  fan  is 
shown  in  Fig.  146.  This  is  known  as  the 
cone  fan,  and  is  commonly  placed  in  an 
opening  in  a  brick  wall,  and  discharges  air 
from  its  entire  periphery  into  a  room  called 
a  plenum  chamber,  with  which  the  various 

distributing  ducts  connect. 

This  fan  is  often    made    double  by  placing  two  wheels  back  to 


Fig.  141.    Centrifugal  Fan  or  Blower. 


Fig.  142.  Illustrating  Action 
of  Centrifugal  Fan.  The 
Arrows  Show  the  Path  of 
the  Air. 


356 


HEATING  AND  VENTILATION 


161 


back  and  surrounding  them  with  a  steel  casing  in  a  similar  manner 
to  the  one  shown  in  Fig.  143. 

Cone  fans  are  particularly  adapted  to  church  and  schoolhouse 
work,  as  they  are  capable  of  moving  large  volumes  of  air  at  moderate 
speeds. 

Fig.  147  shows  a  form  of  small  direct-connected  exhauster  com- 
monly used  for  ventilating  toilet-rooms,  chemical  hoods,  etc. 

Centrifugal  fans  are  used  almost  exclusively  for  supplying  air 
for  the  ventilation  of  buildings,  and  for  forced-blast  heating.  They 
are  also  used  as  exhausters 
for  removing  the  air  from 
buildings  in  cases  where 
there  is  considerable  resist- 
ance due  to  the  small  size 
or  excessive  length  of  the 
discharge  ducts. 

General  Proportions. 
The  general  form  of  a  fan 
wheel  is  shown  in  Fig.  141, 
which  represents  a  single 
spider  wheel  with  curved 
blades.  Those  over- 4  feet 
in  diameter  usually  have 
two  spiders,  while  fans  of 
large  size  are  often  pro- 
vided with  three  or  more. 
The  number  of  floats  or 
blades  commonly  varies 
from  six  to  twelve,  depending  upon  the  diameter  of  the  fan.  They 
are  made  both  curved  and  straight;  the  former,  it  is  claimed,  run 
more  quietly,  but,  if  curved  too  much,  will  not  work  so  well  against 
a  high  pressure  as  the  latter  form. 

The  relative  proportions  of  a  fan  wheel  vary  somewhat  in  the 
case  of  different  makes.  The  following  are  averages  taken  from  fans 
of  different  sizes  as  made  by  several  well-known  manufacturers  for 
general  ventilating  and  similar  work: 

Width  of  fan  at  center  =  Diameter  X  .52 

Width  of  fan  at  perimeter  =  Width  at  center  X  -8 

Diameter  of  inlet  =  Diameter  of  wheel  X  .68 


Fig.  143.    Centrifugal  Fan  with  Casing. 


357 


HEATING  AND  VENTILATION 


Fig.  144.    Combined  Heater  and  Centrifugal  Fan  with  Direct-Connected  Engine. 


Fig.  145.    Centrifugal  Fan  in  "Three-Quarter  Housing."    Used  where  Headroom  is 
Limited;  Extra  Space  Provided  by  Pit  under  Floor-Level. 


358 


HEATING  AND  VENTILATION  . 


163 


Fans  are  made  both  with  double  and  with  single  inlets,  the 
former  being  called  blowers  and  the  latter  exhausters.  The  size  of 
a  fan  is  commonly  expressed  in  inches,  which  means  the  approximate 
height  of  the  casing  of  a  full-housed  fan.  The  diameter  of  the  wheel 
is  usually  expressed  in  feet,  and  can  be  found  in  any  given  case  by 
dividing  the  size  in  inches  by  20.  For  example,  a  120-inch  fan  has  a 
wheel  120  -r-  20  =  6  feet  in  diameter. 


Fig.  146.    "Cone"  Fan. 


Discharges  through  Opening  in  Wall  into  a  " 
Connecting  with  Distributing  Ducts. 


Plenum  Chamber" 


Theory  of  Centrifugal  Fans.  The  action  of  a  fan  is  affected 
to  such  an  extent  by  the  various  conditions  under  which  it  operates, 
that  it  is  impossible  to  give  fixed  rules  for  determining  the  exact 
results  to  be  expected  in  any  particular  instance.  This  being  the 
case,  it  seems  best  to  take  up  the  matter  briefly  from  a  theoretical 


359 


164 


HEATING  AND  VENTILATION 


standpoint,   and   then  show  what  corrections  are  necessary  in  the 
case  of  a  given  fan  under  actual  working  conditions. 

There  are  various  methods  for  determining  the  capacity  of  a 
fan  at  different  speeds,  and  the  power  necessary  to  drive  it;  each 
manufacturer  has  his  own  formula?  for  this  purpose,  based  upon 
tests  of  his  own  particular  fans.  The  methods  given  here  apply 
in  a  general  way  to  fans  having  proportions  which  represent  the 
average  of  several  standard  makes;  and  the  results  obtained  will  be 


Fi^'.  147.   Small,  Direct-Connected  Exhauster  for  Ventilating  Toilet-Rooms,  Chemical 
Hoods,  etc. 

found    to   correspond    well    with    those   obtained    in    practice   under 
ordinary  conditions. 

As  already  stated,  the  rotation  of  a  fan  of  this  type  sets  in  motion 
the  air  between  the  blades,  which,  by  the  action  of  centrifugal  force, 
is  delivered  at  the  periphery  of  the  wheel  into  the  casing  surrounding 
it.  As  the  velocity  of  flow  through  the  discharge  outlet  depends 
upon  the  pressure  or  head  within  the  casing,  and  this  in  turn  upon 
the  velocity  of  the  blades,  it  becomes  necessary  to  examine  briefly 
into  the  relations  existing  between  these  quantities. 


HEATING  AND  VENTILATION 


165 


Pressure.  The  pressure  referred  to  in  connection  with  a  fan, 
is  that  in  the  discharge  outlet,  and  represents  the  force  which  drives 
the  air  through  the  ducts  and  flues.  The  greater  the  pressure  with  a 
given  resistance  in  the  pipes,  the  greater  will  be  the  volume  of  air 
delivered;  and  the  greater  the  resistance,  the  greater  the  pressure 
required  to  deliver  a  given  quantity. 

The  pressure  within  a  fan  casing  is  caused  by  the  air  being 
thrown  from  the  tips  of  the  blades,  and  varies  with  the  velocity  of 
rotation;  that  is,  the  higher  the  speed  of  the  fan,  the  greater  will  be 
the  pressure  produced.  Where  the  dimensions  of  a  fan  and  casing 
are  properly  proportioned,  the  velocity  of  air-flow  through  the  outlet 
will  be  the  same  as  that  of  the  tips  of  the  blades,  and  the  pressure 
within  the  casing  will  be  that  corresponding  to  this  velocity. 

Table  XXXIII  gives  the  necessary  speed  for  fans  of  different 
diameters  to  produce  different  pressures,  and  also  the  velocity  of  air- 
flow due  to  these  pressures. 

TABLE   XXXIII 
Fan  Speeds,  Pressures,  and  Velocities  of  Air-Flow 


7.  j. 

H 

•  Eg 

' 

can 

*r*s 

£3* 

3 

4 

5 

6 

7 

8 

9 

10 

S>« 

£° 

REVOLUTIONS  PER  MINUTE 

1 

274 

206 

164 

137 

117 

103 

92 

82 

2,585 

336 

252 

202 

168 

144 

126 

112 

101 

3,165 

1 

338 

291 

232 

194 

166 

146 

129 

116 

3,653 

1 

433 

325 

260 

217 

186 

163 

144 

130 

4,084 

The  application  of  this  table  will  be  made  plain  by  a  brief  dis- 
cussion .of  blast  area. 

Blast  Area.  When  the  outlet  from  a  fan  casing  is  small,  the  air 
will  pass  out  with  a  velocity  equal  to  that  of  the  tips  of  the  blades ;  and 
the  pressure  within  the  casing  will  be  that  corresponding  to  the 
tip  velocity.  That  is,  a  3-foot  fan  wheel  revolving  at  a  speed  of  274 
revolutions  per  minute  will  produce  a  pressure  within  the  fan  casing 
of  I  ounce  per  square  inch,  and  will  cause  a  velocity  of  flow  through 
the  discharge  outlet  of  2,585  feet  per  minute  (see  Table  XXXIII). 


361 


166  HEATING  AND  VENTILATION 

Now,  if  the  opening  be  slowly  increased,  while  the  speed  of  the  fan 
remains  constant,  the  air  will  continue  to  flow  with  the  same  velocity 
until  a  certain  area  of  outlet  is  reached.  If  the  outlet  be  still  further 
increased,  the  pressure  in  the  casing  will  begin  to  drop,  and  the 
velocity  of  outflow  become  less  than  the  tip  velocity.  The  effective 
area  of  outlet  at  the  point  when  this  change  begins  to  take  place,  is 
called  the  blast  area  or  capacity  area  of  the  fan.  This  varies  some- 
what with  different  types  and  makes  of  fans;  but  for  the  common 
form  of  blower,  it  is  approximately  £  of  the  projected  area  of  the  fan 

opening  at  the  periphery — that  is,  — - — ,  in  which  D  is  the  diameter 

of  the  fan  wheel,  and  w  its  width  at  the  periphery.  It  has  already 
been  stated  under  "General  Proportions"  that  W  =  .  52  D,  and  w  =  .8 

D  X  .8  IF     Dx  -8X  -5279 

\\  ;  so  that  we  may  write  A  = —  — - —       —  =  .14  D~, 

o  o 

in  which  A  =  the  blast  area,  and  D  the  diameter  of  the  fan. 

As  a  matter  of  fact,  the  outlet  of  a  fan  casing  is  always  made 
larger  than  the  blast  area;  and  the  result  is  that  the  pressure  drops 
below  that  due  to  the  tip  velocity,  and  the  velocity  of  flow  through 
the  outlet  becomes  less  than  that  given  in  the  last  column  of  Table 
XXXIII  for  any  'given  speed  of  fan. 

Effective  Area  of  Outlet.  The  size  of  discharge  outlet  varies 
somewhat  for  different  makes;  but  for  a  large  number  of  fans  ex- 
amined it  was  found  to  average  about  2.22  times  the  blast  area 
as  computed  by  the  above  method.  When  air  or  a  liquid  flows 
through  an  orifice,  the  stream  is  more  or  less  contracted,  depending 
upon  the  form  of  the  orifice. 

In  the  case  of  a  fan  outlet,  the  effective  area  may  be  taken  as  about 
.X  of  the  actual  area.  This  makes  the  effective  area  of  a  fan  outlet 
equal  to  .8  X  2.22  =  1.78  times  the  blast  area. 

Table  XXXIV  gives  the  effective  areas  of  fans  of  different 
diameter  as  computed  by  the  above  method.  That  is,  Effective 
area  -  .147J2  X  1.78  =  .25Z)2. 

Speed.  We  have  seen  that  when  the  discharge  outlet  is  made 
larger  than  the  blast  area,  the  pressure  within  the  fan  casing  drops 
below  that  due  to  the  tip  velocity;  so  that,  in  order  to  bring  the  pres- 
sure up  to  its  original  point,  the  speed  of  the  fan  must  be  increased 
above  that  given  in  Table  XXXIII. 


362 


EXCELSIOR  PATTERN  RADIATOR  USED  IN  THE  INDIRECT  METHOD 
OF  WARMING 

American  Radiator  Company 


METHOD  OF  INDIRECT  WARMING  AND  VENTILATION,  SHOWING  ROTARY 
CIRCULATION  OF  AIR 

American  Radiator  Company 


HEATING  AND  VENTILATION  167 

TABLE  XXXIV 
Effective  Areas  of  Fans 


EFFECTIVE  AREA  OF  OUTLET,  IN 

SQUARE  FEET 

3 

2.3 

4 

4.0   ' 

5 

6.3 

6 

9.1 

7 

12.3 

8 

16.0 

9 

20.4 

10 

25.2 

Tests  upon  a  fan  of  practically  "the  same  proportions  as  those 
previously  given,  show  that,  when  the  effective  outlet  area  is  made 
1 . 78  the  blast  area,  the  speed  must  be  increased  1 . 2  times  in  order 
to  keep  the  pressure  at  the  same  point  as  when  the  outlet  is  equal 
to  or  less  than  the  blast  area. 

Capacity.  The  capacity  of  a  fan  is  the  volume  of  air  discharged 
in  a  given  time,  and  is  usually  expressed  in  cubic  feet  per  minute. 
It  is  equal  to  the  effective  area  of  discharge  multiplied  by  the  velocity 
of  flow  through  it. 

Example.  At  what  speed  must  a  6-foot  fan  be  run  to  maintain  a  pres- 
sure of  J  ounce,  and  what  volume  of  air  will  be  delivered  per  minute? 

From  Table  XXXIII  we  find  that  a  6-foot  fan  must  run  at  a 
speed  of  194  revolutions  per  minute  to  maintain  the  given  pressure 
when  the  outlet  is  equal  to  the  blast  area,  or  194  X  1 .2  =  233  revo- 
lutions per  minute  under  actual  conditions.  The  velocity  of  flow 
through  the  outlet  at  \  ounce  pressure,  is  3,653  feet  per  minute  (Table 
XXXIIJ) ;  and  the  effective  area  of  outlet  of  a  6-foot  fan  is  9 . 1  square 
feet  (Table  XXXIV).  Therefore  the  volume  of  air  delivered  per 
minute  is  equal  to  9.1  X  3,653  -  33,242  cubic  feet. 

Example.  It  is  desired  to  move  52,000  cubic  feet  of  air  per 
minute  at  a  pressure  of  \  ounce.  What  size  and  speed  of  fan  will 
be  required?  Looking  in  Table  XXXIII,  we  find  that  the  velocity 
through  the  fan  outlet  for  ^-ounce  pressure  is  2,585,  which  calls  for 
an  outlet  area  of  52,000  -^-  2,585  =  20.1  square  feet.  Looking  in 
Table  XXXIV,  we  find  this  corresponds  very  nearly  to  a  9-foot  fan, 
which  is  the  size  called  for.  Referring  again  to  Table  XXXIII,  the 
speed  necessary  to  maintain  the  required  pressure  under  the  given 
conditions  is  found  to  be  92  X  1 .2  =  110  revolutions  per  minute. 


If.S  HEATING  AXD  VENTILATION 

Effect  of  Resistance.  Thus  far  it  has  been  assumed  that  the 
fan  was  discharging  into  the  open  air  against  atmospheric  pressure. 
The  effect  of  adding  a  resistance  by  connecting  it  with  a  series  of 
ventilating  ducts,  is  the  same  as  partially  closing  the  discharge  outlet. 
Carefully  conducted  tests  upon  this  type  of  fan  have  shown  that  the 
reduction  of  air-flow  is  very  nearly  in  proportion  to  the  reduction 
of  the  discharge  area.  That  is,  if  the  outlet  of  the  fan  is  closed  to 
one-half  its  original  area,  the  quantity  of  air  discharged  will  be  prac- 
tically one-half  that  delivered  by  the  fan  with  a  free  opening.  The 
effect  of  attaching  a  fan  to  the  ventilating  flues  of  a  building  like  a 
schoolhouse,  church,  or  hall,  where  the  ducts  have  easy  bends  and 
where  the  velocity  of  air-flow  through  them  is  not  over  1,000  to  1,200 
feet  per  minute,  is  about  the  same  as  reducing  the  outlet  20  per  cent. 
For  factories  with  deep  heaters  and  smaller  ducts,  where  the  velocity 
runs  up  to  1,500  or  1,800  feet  per  minute,  the  effect  is  equivalent  to 
closing  the  outlet  at  least  30  per  cent,  and  even  more  in  very  large 
buildings. 

For  schoolhouses  and  similar  work  a  fan  should  not  be  run  much 
above  the  speed  necessary  to  maintain  a  pressure  of  §  ounce  at  the 
outlet.  Higher  speeds  are  accompanied  with  greater  expenditure  of 
power,  and  are  likely  to  produce  a  roaring  noise  or  to  cause  vibration. 
A  much  lower  speed  does  not  provide  sufficient  pressure  to  give  proper 
control  of  the  air-distribution  during  strong  winds.  For  factories, 
a  higher  pressure  of  J  to  :]  ounce  is  more  generally  employed. 

Actually  the  pressure  is  increased  slightly  by  restricting  the  out- 
let at  constant  speed ;  but  this  is  seldom  taken  into  account  in  venti- 
lating work,  as  volume,  speed,  and  power  are  the  quantities  sought. 

E.rinnjilc.  A  school  building  requires  32.000  cubic  feet  of  air  per  min- 
ute. What  size  and  speed  of  fan  will  be  required? 

If  the  resistance  of  the  ducts  and  flues,  is  equivalent  to  cutting 
down  the  discharge  outlet  20  per  cent,  we  must  make  the  computa- 
tions for  a  fan  which  will  discharge  32,000  -r-  .8  =  40,000  cubic  feet 
in  free  air. 

Looking  in  Table  XXXIII,  we  find  the  velocity  for  f-ounce 
pressure  to  be  3,165  feet  per  minute;  therefore  the  size  of  fan  outlet 
must  be  40,000  -r  3,105  =  12.6  square  feet,  which,  from  Table 
XXXIV,  we  find  corresponds  very  nearly  to  a  7-foot  fan. 


364 


HEATING  AND  VENTILATION  169 

Referring  again  to  Table  XXXIII,  the  required  speed  is  found 
to  be  144  X  1.2  =  173  revolutions  per  minute. 

Example.  A  factory  requires  21,000  cubic  feet  of  air  per  minute  for 
wanning  and  ventilating.  What  size  and  speed  of  fan  will  be  required? 

21,000  -f-  .7  =  30,000,  the  volume  to  provide  for  with  a  fan 
discharging  into  free  air.  Assuming  a  pressure  of  f  ounce,  the  veloc- 
ity will  be  4,084  feet  per  minute,  from  which  the  area  of  outlet  is 
found  to  be  30,000  H-  4,084  =  7. 3- square  feet.  This,  we  find,  does 
not  correspond  to  any  of  the  sizes  given  in  Table  XXXIV.  As 
standard  fans  are  not  usually  made  in  half-sizes  above  5  feet,  we 
shall  use  a  5-foot  fan  and  run  it  at  a  higher  speed. 

A  5-foot  fan  has  an  outlet  area  of  6 . 3  square  feet,  and  at  f-ounce 
pressure  it  would  deliver  6 . 3  X  4,084  =  25,729  cubic  feet  of  air  per 
minute,  at  a  speed  of  260  X  1.2  =  312  revolutions  per  minute. 
The  volume  of  air  delivered  by  a  fan  varies  approximately  as  the 
speed;  so,  in  order  to  bring  the  volume  up  to  the  required  30,000,  the 
speed  must  be  increased  by  the  ratio  30,000  -r  25,729  -  1.16, 
making  the  final  speed  312  X  1.16  =  362  revolutions  per  minute. 
In  the  same  way,  a  6-foot  fan  could  have  been  used  and  run  at  a 
proportionally  lower  speed. 

Power  Required.  The  work  done  by  a  fan  in  moving  air  .is 
represented  by  the  pressure  exerted,  multiplied  by  the  distance  through 
which  it  acts. 

Table  XXXV  gives  the  horse-power  required  for  moving  the 
air  which  will  flow  through  each  square  foot  of  the  effective  outlet 
area,  under  different  pressures. 

This  table  gives  only  the  power  necessary  for  moving  the  air, 
and  does  not  take  into  consideration  the  friction  of  the  air  in  passing 
through  the  fan,  nor  that  of  the  fan  itself. 

The  efficiency  of  a  fan  varies  with  the  speed,  the  size  of  outlet, 
and  the  pressure  against  which  the  fan  is  working.  Under  favorable 
conditions,  with  properly  proportioned  fans,  we  may  count  on  an 
efficiency  of  about  .35. 

Example.  What  horse-power  will  be  required  to  drive  an  8-foot  fan  at 
such  a  speed  as  to  maintain  a  pressure  of  £  ounce? 

An  8-foot  fan  has  an  6utlet  area  of  16  square  feet  (Table  XXXIV) ; 
and  from  Table  XXXV  we  find  that  .5  horse-power  is  required  to 
move  the  air  which  will  flow  through  each  square  foot  of  outlet  under 


365 


170  HEATING  AND  VENTILATION 

TABLE  XXXV 

Power  Required  for  Moving  Air  under  Different  Pressures 


HORSE-POWER     FOR    MOVING    AlR    WHICH    WILL 
FLOW   THROUGH   E.A.CH   SQUARE    FOOT  OF 

EFFECTIVE  OUTLET  AREA 

1 

.18 
.33 
.50 

.70 

^-ounce  pressure.  Therefore  the  power  required  to  move  the  air 
alone  is  10  X  .5  =  8,  and  the  total  horse-power  is  8  -=-  .35  =  23. 

Effect  of  Resistance.  In  the  above  case,  it  is  assumed  that  the 
fan  is  discharging  into  free  air.  If  a  resistance  is  added,  the  effect 
is  the  same  as  partially  closing  the  outlet,  and  the  volume  of  air 
moved  and  the  horse-power  required  are  both  reduced  in  very  nearly 
the  same  proportion.  This  reduction,  as  already  stated,  may  be 
taken  as  20  per  cent  for  schoolhouse  and  similar  work,  and  30  per 
cent  for  factories. 

For  example,  if  the  fan  just  considered  was  to  be  used  for  venti- 
lating a  schoolhouse,  delivering  air  under  a  pressure  of  }  ounce,  the 
necessary  horse-power  would  be 'only  23  X  .8  =  18.4.  If  used  for 
a  factory,  delivering  air  under  a  pressure  rf  £  ounce,  the  required 

horse-power  would  be ^~-~~~  X  -7  =  22.3. 

General  Rules.     The  methods  above  described  may  be  briefly 
expressed  as  follows: 
CAPACITY — Q  =  A  X  r  X  F,  in  which 
Q  =  Cubic  feet  of  air  per  minute: 
A  =  Effective  area  of  fan  outlet  (Table  XXXIV); 
?•  =  Velocity  of  flow  through  outlet; 

(3,165  (j-ounce  pressure)-for  schoolhouses,  etc.; 
(4,084  (ij -ounce  pressure)  for  factories; 
p  _  j  -8  for  schoolhouses,  etc.; 

|  .7  for  factories. 

SPEED— Take   the   speed  from   Table   XXXIII,   corresponding  to  the  given 
pressure  and  size  of  fan,  and  multiply  by  1.2. 

HOUSE-POWER— H.P.  =  -1  x  P  x  F     in  whieh 
.3o 

H.P.  =  Horse-power; 

A  =  Effective  area  of  fan  outlet; 

p  =  Horse-power  to  move  air  which  will  flow  through  1  square  foot  of  fan 
outlet  under  given  pressure  (Table  XXXV); 


HEATING  AND  VENTILATION     .  171 

_  j  .33  for  schoolhouses,  etc.; 

j  .7  for  factories. 
„  _._  j  .8  for  schoolhouses,  etc.;' 
~  1  -7  for  factories. 

EXAMPLES 

1.  A  schoolhouse  requires  an  air-supply  of  30,000  cubic  feet 
per  minute.      What  will  be  the  required  size  of  fan,  its  speed,  and 
the  H.  P.  of  engine  to  drive  it?  f  7  ft.  in  diameter. 

Axs.  «  173  r.  p.  m. 
[9  H.P. 

2.  What  will  be  the  size  and  speed  of  fan,  and  horse-power  of 
engine,  to  heat  and  ventilate  a  factory  requiring  1,080,000  cubic  feet 
of  air  per  hour?  f6ft.  in  diameter. 

ANS.  j  260  r.  p.  m. 

[8.8  H.P. 

General  Relations.  The  following  general  relations  between  the 
volume,  pressure,  and  power  will  often  be  found  useful  in  deciding 
upon  the  size  of  a  fan: 

(1)  The  volume  of  air  delivered  varies  directly  as  the  speed  of  the  fan; 
that  is,  doubling  the  number  of  revolutions  doubles  the  volume  of  air  de- 
livered. 

(2)  The  pressure  varies  as  the  square  of  the  speed.     For  example,  if 
the  speed  is  doubled,  the  pressure  is  increased  2X2  =  4  times;  etc. 

(3)  The  power  required  to  run*  the  fan  varies  as  the  cube  of  the  speed. 
Thus,  if  the  speed  is  doubled,  the  power  required  is  increased  2X2X2  =  8 
times;  etc. 

The  value  of  a  knowledge  of  these  relations  may  be  illustrated 
by  the  following  example: 

Suppose  for  any  reason  it  were  desired  to  double  the  volume  of 
air  delivered  by  a  certain  fan.  At  first  thought  we  might  decide  to 
use  the  same  fan  and  run  it  twice  as  fast;  but  when  we  come  to  con- 
sider the  power  required,  we  should  find  that  this  would  have  to  be 
increased  8  times,  and  it  would  probably  be  much  cheaper  in  the 
long  run  to  put  in  a  larger  fan  and  run  it  at  lower  speed. 

Disc  or  Propeller  Fans.  When  air  is  to  be  moved  against  a  very 
slight  resistance,  as  in  the  case  of  exhaust  ventilation,  the  disc  or  pro- 
peller type  of  wheel  may  be  used.  This  is  shown  in  different  forms 
in  Figs.  149  and  150.  This  type  of  fan  is  light  in  construction,  re- 
quires but  little  power  ai  low  speeds,  and  is  easily  erected.  It  may  be 


367 


172 


HEATING  AND  VENTILATION 


conveniently  placed  in  the  attic  or  upper  story  of  a  building,  where 
it  may  be  driven  either  by  a  direct-  or  belt-connected  electric  motor. 
Fig.  148  shows  a  fan  equipped  with  a  direct-connected  motor,  and 
Fig.  151  the  general  arrangement  when  a  belted  motor  is  used.  These 
fans  are  largely  used  for  the  ventilation  of  toilet  and  smoking  rooms, 
restaurants,  etc.,  and  are  usually  mounted  in  a  wall  opening,  as  shown 
in  Fig.  151.  A  damper  should  always  be  provided  for  shutting  off 
the  opening  when  the  fan  is  not  in  use.  The  fans  shown  in  Figs.  149 
and  150  are  provided  with  pulleys  for  belt  connection. 


Propeller  Fan  Direct-Connected  to  Moti 


Fans  of  this  kind  are  often  connected  with  the  main  vent  flues 
of  large  buildings,  such  as  schools,  halls,  churches,  theaters,  etc., 
and  are  especially  adapted  for  use  in  connection  with  gravity  heating 
systems.  They  are  usually  run  by  electric  motors,  and  as  a  rule  are 
placed  in  positions  where  an  engine  could  not  be  connected  and  also 
in  buildings  where  steam  pressure  is  not  available. 

Capacity  of  Disc  Fans.  The  capacity  of  a  disc  fan  varies  greatly 
with  the  type  and  the  conditions  under  which  it  operates.  The  rated 


368 


HEATING  AND  VENTILATION 


173 


capacities  usually  given  in  catalogues  are  for  fans  revolving  in  free 
air — that  is,  mounted  in  an  opening  without  being  connected  with 
ducts  or  subjected  to  other  frictional  resistance. 

As  the  capacity  and  necessary  power  are  so  dependent  upon  the 
resistance  to  be  overcome,  it  is  difficult  to  give  definite  rules  for 
determining  them.  The  following  data,  based  upon  actual  tests. 


.  149.    Another  Form  of  Propeller  Fan,  with  Special  Type  of  Blade. 


apply  to  fans  working  against  a  resistance  such  as  would  be 
produced  by  connecting  with  a  system  of  ducts  of  medium  length 
through  which  the  air  was  drawn  at  a  velocity  not  greater  than  600 
or  800  feet  per  minute.  Under  these  conditions,  a  good  type  of  fan 
will  propel  the  air  in  a  direction  parallel  to  the  shaft  a  distance  equal  to 
about  .  7  of  its  diameter  at  each  revolution  ;  and  from  this  we  have 
the  equation  : 


369 


174 


HEATING  AND  VENTILATION 


Q  =  .7  D  X  R  X  A, 

Q  —  Cubic  feet  of  air  discharged  per  minute; 

D  =  Diameter  of  fan,  in  feet ; 

7?  =  Revolutions  per  minute; 

A  =  Area  of  fan,  in  square  feet. 
In  order  to  obtain  the 
best  results,  the  linear  velocity 
/>f  air-flow  through  the  fan 
should  range  from  800  to  1 ,200 
feet  per  minute. 

Table  XXXVI  gives  the 
revolutions  per  minute  for 
fans  of  different  diameter  to 
produce  a  linear  velocity  of 
1,000  feet,  the  volume  deliv- 
ered at  this  speed,  and  the 
horse-power  required . 

The  horse-power  is  com- 
puted by  allowing  .14  II.  P. 
for  each  1,000  cubic  feet  of 
air  moved,  when  the  velocity 
through  the  fan  is  800  feet 
per  minute;  .10  II.  P.  for 
1,000  feet  velocity;  and  .1811.  P.  for  1,200  feet  velocity.  These 
factors  are  empirical,  and  based  on  tests. 


Fig.  150.     Propeller  Fan  with  Wheel  on  Shaft 
for  Belt  Connection. 


Fan  Belt-Connected  to  Motor. 


Example.  Assuming  a  velocity  of  800  feet  per  minute  through  a  4-foot 
fan,  what  volume  will  be  delivered  per  minute,  and  what  speed  and  horse- 
power will  be  required  ? 


370 


HEATING  AND  VENTILATION 


175 


TABLE  XXXVI 
Disc  Fans,  their  Capacity,  Speed,  etc. 


DIA.  OF  FAN,  IN 
INCHES 

REV.   PER  MIN. 

CUBIC  FEET  OF    AIR 
MOVED 

HORSE-POWER 
REQUIRED 

18 

952 

1,700 

.27 

24 

.      716 

3,100 

.50 

30 

572 

4,900 

.78 

'36 

476 

7,100 

1.2 

42 

408 

9,400 

1.5 

48 

343 

12,000 

1.9 

54 

317 

15,800 

2.5 

60 

286 

19,400 

3.1 

72 

238 

28,300 

4.5 

The  area  of  a  4-foot  fan  is  12.5  square  feet;  and  at  800  velocity 
the  volume  would  be  12.5  X  800  -  10,000  cubic  feet.  Next  solve 
for  the  speed  by  the  equation  Q  =  .ID  X  R  X  A,  which,  when 
transposed,  takes  the  form 

;?-         Q 

~  .1  D  X  A 

Substituting  the  known  quantities,  we  have: 

_        10,000         _ 
~.7X4X  12.5  ~ 

The  horse-power  is  10  X  .14  =  1.4. 

Fan  Engines.  A  simple,  quiet-running  engine  is  desirable 
for  use  in  connection  with  a  fan  or  blower.  The  engine  may  be  either 
horizontal  or  vertical;  and  for  schoolhouse  and  similar  work,  should 
be  provided  with  a  large  cylinder,  so  that  the  required  power  may 
be  developed  without  carrying  a  boiler  pressure  much  above  30 
pounds.  In  some  cases,  cylinders  of  such  size  are  used  that  a  boiler 
pressure  of  12  or  15  pounds  is  sufficient.  The  quantity  of  steam 
which  an  engine  consumes  is  of  minor  importance,  as  the  exhaust  can 
be  turned  into  the  coils  and  used  for  heating  purposes.  If  space 
allows,  the  engine  should  always  be  belted  to  the  fan.  Where  it  is 
direct-connected,  as  in  Fig.  144,  there  is  likely  to  be  trouble  from 
noise,  as  any  slight  looseness  or  pounding  in  the  engine  will  be  com- 
municated to  the  air-ducts,  and  the  sound  will  be  carried  to  the  rooms 


371 


17(5 


HEATING  AND  VENTILATION 


above.     Figs.  152  and  153  show  common  forms  of  fan  engines.     The 
latter  is  especially  adapted  to  this  purpose,  as  all  bearings  are  enclosed 


Fig.  152     A  Common  Form  of  Fan  Engine. 


and  protected  from  dust  and  grit.     A  horizontal  engine  for  fan  use 
is  shown  in  Fig.  154. 

In  case  an  engine  is  belted,  the  distance  between  the  shafts  of 
the  fan  and  engine  should  not  in  general  be  much  less  than  10  feet 


372 


HEATING  AND  VENTILATION 


177 


for  fans  up  to  7  or  8  feet  in  diameter,  and  12  feet  for  those  of  larger 
size.  When  possible,  the  tight  or  driving  side  of  the  belt  should 
be  at  the  bottom,  so  that  the  loose  side,  coming' on  top,  will  tend  to 
wrap  around  the  pulleys  and  so  increase  the  arc  of  contact. 

Motors.     Electric   motors   are   especially   adapted   for  use   in 
connection  with  fans.     This  method  of  driving  is  more  expensive 


Fig.  153.    Another  Form  of  Fan  Engine,  with  Bearings  Enclosed  to  Protect  Them 
from  Dust  and  Grit. 

than  by  the  use  of  an  engine,  especially  if  electricity  must  be  pur- 
chased from  outside  parties;  but  if  the  building  contains  its  own 
power  plant,  so  that  the  exhaust  steam  can  be  utilized  for  heating, 
the  convenience  and  simplicity  of  motor-driven  fans  often  more  than 
offset  the  additional  cost  of  operation. 


373 


178 


HEATING  AND  VENTILATION 


Direct-connected  motors  are  always  preferable  to  belted,  if  a 
direct  current  is  available,  on  account  of  greater  quietness  of  action. 
This  is  due  both  to  the  slower  speed  of  the  motor  and  to  the  absence 
of  belts. 

Sufficient  speed  regulation  can  be  obtained  with  direct -connected 
machines,  without  excessive  waste  of  energy,  by  the  use  of  a  rheostat. 

If  a  direct  current  is  not  available,  and  an  alternating  current 
must  be  used,  the  advantages  of  electric  driving  are  greatly  reduced, 
as  high-speed  motors  with  belts  must  be  employed,  and,  further- 
more, satisfactory  speed  regulation  is  not  easily  attainable. 


Fig.  154.    Horizontal  Engine  for  Fan  Use. 

Area  of  Ducts  and  Flues.  \Vith  the  blower  type  of  fan,  the  size 
of  the  main  ducts  may  be  based  on  a  velocity  of  1,200  to  1,500  feet  per 
minute;  the  branches,  on  a  velocity  of  1,000  to  1,200  feet  per  minute, 
and  as  low  as  GOO  to  SOO  feet  when  the  pipes  are  small.  Flue  veloci- 
ties of  500  to  700  feet  per  minute  may  be  used,  although  the  lower 
velocity  is  preferable.  The  size  of  the  inlet  register  should  be  such 
that  the  velocity  of  the  entering  air  will  not  exceed  about  300  feet  per 
minute.  The  velocity  between  the  inlet  windows  and  the  fan.  or 
heater  should  not  exceed  about  800  feet. 

The  air-ducts  and  flues  are  usually  made  of  galvanized  iron,  the 


374 


HEATING  AND  VENTILATION 


179 


ducts  being  run  at  the  basement  ceiling.     No.  20  and  No.  22  iron 
is  used  for  the  larger  sizes,  and  No.  24  to  No.  28  for  the  smaller. 

Regulating  dampers  should 
be  placed  in  the  branches  lead-  *• 
ing  to  each  flue,  for  increasing  or 
reducing  the  air-supply  to  the 
different  rooms.  Adjustable  de- 
flectors are  often  placed  at  the 
fork  of  a  pipe- for  the  same  pur- 
pose. One  of  these  is  shown  in 
Fig.  155. 

Fig.  156  illustrates  a    com- 
mon   arrangement    of    fan    and 
heater  where  the  type  of  heater  Fig.155.  Adjustable  Deflector  Placed  at  Fork 
shown  in  Fig,  138  is  used;  and  of  pipe  to  Regulate  Air-supPiy. 

Fig.  157  is  a  self-contained  apparatus  in  which  the  heater  is  inclosed 

in  a  steel  casing.     ' 

Factory    Heating.    The    application    of   forced    blast    for   the 

warming  of  factories  and 
shops,  is  shown  in  Figs. 
158  and  159.  The  pro- 
portional heating  surface 
in  this  case  is  generally 
expressed  in  the  'number 
of  cubic  feet  in  the 
building  for  each  linear 
foot  of  1-inch  steam 
pipe  in  the  heater.  On 
this  basis,  in  factory 
practice,  with  all  of  the 
air  taken  from  out  of 
doors,  there  are  generally 
allowed  from  100  to  150 
cubic  feet  of  space  per 

Fig.  156.    Common  Arrangement  of  Fan  with  Heater       foot  of  P^P6'  according  as 

of  Type  Shown  in  Fig.  138.  exhaust    or    live    steam 

is   used,   live   steam    in    this  case  indicating  steam  of  about   80 
pounds  pressure.     If  practically  all   the  air  is   returned   from  the 


375 


180 


HEATING  AND  VENTILATION 


buildings  to  the  heater,  these  figures  may  be  raised  to  about  140  as  a 
minimum,  and  possibly  200  as  a  maximum,  per  foot  of  pipe.     The 


heaters  in  Table  XXXI  may  be  changed  to  linear  feet  of  1  inch  pipe 
by  multiplying  the  numbers  in  column  three  (suuare  feet  of  surface) 
bv  three. 


376 


HEATING  AND  VENTILATION 


181 


EXAMPLES  FOR  PRACTICE 

1.     A  machine  shop  100  feet  long  by  50  feet  wide  and  having  3 
stories,  each  10  feet  high,  is  to  be  warmed  by  forced  blast,  using 


Pig.  158.    Illustrating  Application  of  Forced  Blast  for  Warming  a  Factory. 

exhaust  steam  in  the  heater.  The  air  is  to  be  returned  to  the  heater 
from  the  building,  and  the  whole  amount  contained  in  the  building 
is  to  pass  through  the  heater  every  15  minutes.  What  size  of  blower 


377 


182 


HEATING  AND  VENTILATION 


will  be  required,  and  what  will  be  the  H.  P.  of  the  engine  required  to 
run  it?  How  many  linear  feet  of  1-inch  pipe  should  the  heater  con- 
tain? 

J  4-foot    blower. 
Axs.  -j  6  H.  P.  engine. 

[  1,071   feet  of  pipe. 


Fig.  159.    Centrifugal  Blower  Producing  Forced  Blast  for  Heating  a  Shop. 

2.  Find  the  size  of  blower,  engine,  and  heater  for  a  factory 
200  feet  long,  60  feet  wide,  and  having  4  stories,  each  10  feet  high, 
using  live  steam  at  80  pounds  pressure  in  the  heater,  and  changing 
the  air  every  20  minutes  by  taking  in  cold  air  from  out  of  doors. 

f  6-foot  blower. 
Axs.  \  13  H.  P.  engine. 

[3,200  feet   of  pipe. 


378 


•UTTLE  GIANT  BOILER  AS  INSTALLED  FOR  FIRE  DEPARTMENT  SERVICE 

Pierce,  Butler  &  Pierce  Mfg.  Co. 


HEATING  AND  VENTILATION 


183 


In  using  this  method  of  computation,  judgment  must  be  employed, 
which  can  come  only  from  experience.  The  figures  given  are  for 
average  conditions  of  construction  and  exposure. 

Double=Duct  System.  The  varying  exposures  of  the  rooms  of 
a  school  or  other  building  similarly  occupied,  require  that  more  heat 
shall  be  supplied  to  some  than  to  others.  Rooms  that  are  on  the 
south  side  of  the  building  and  exposed  to  the  sun,  may  perhaps  be 
kept  perfectly  comfortable  with  a  supply  of  heat  that  will  maintain 
a  temperature  of  only  50  or  60  degrees  in  rooms  on  the  opposite  side 
of  the  building  which  are  exposed  to  high  winds  and  shut  off  from  the 
warmth  of  the  sun. 


Fig. 


Hot-Blast  Apparatus  with  Double  Duct  for  Supplying  Air  at  Different  Temper- 
atures to  Different  Parts  of  a  Building. 


With  a  constant  and  equal  air-supply  to  each  room,  it  is  evident 
that  the  temperature  must  be  directly  proportional  to  the  cooling 
surfaces  and  exposure,  and  that  no  building  of  this  character  can  be 
properly  heated  and  ventilated  if  the  temperature  cannot  be  varied 
without  affecting  the  air-supply. 

There  are  two  methods  of  overcoming  this  difficulty: 
The  older  arrangement  consists  in  heating  the  air  by  means  of  a 
primary  coil  at  or  near  the  fan,  to  about  60  degrees,  or  to  the  minimum 
temperature  required  within  the  building.  From  the  coil  it  passes 
to  the  bases  of  the  various  flues,  and  is  there  still  further  heated  as 
required,  by  secondary  or  supplementary  heaters  placed  at  the  base  of 
each  flue. 


379 


HEATING  AND  VENTILATION 


183 


In  using  this  method  of  computation,  judgment  must  be  employed, 
which  can  come  only  from  experience.  The  figures  given  are  for 
average  conditions  of  construction  and  exposure. 

Double=Duct  System.  The  varying  exposures  of  the  rooms  of 
a  school  or  other  building  similarly  occupied,  require  that  more  heat 
shall  be  supplied  to  some  than  to  others.  Rooms  that  are  on  the 
south  side  of  the  building  and  exposed  to  the  sun,  may  perhaps  be 
kept  perfectly  comfortable  with  a  supply  of  heat  that  will  maintain 
a  temperature  of  only  50  or  60  degrees  in  rooms  on  the  opposite  side 
of  the  building  which  are  exposed  to  high  winds  and  shut  off  from  the 
warmth  of  the  sun. 


Fig.  160.    Hot-Blast  Apparatus  with  Double  Duct  for  Supplying  Air  at  Different  Temper- 
atures to  Different  Parts  of  a  Building. 

With  a  constant  and  equal  air-supply  to  each  room,  it  is  evident 
that  the  temperature  must  be  directly  proportional  to  the  cooling 
surfaces  and  exposure,  and  that  no  building  of  this  character  can  be 
properly  heated  and  ventilated  if  the  temperature  cannot  be  varied 
without  affecting  the  air-supply. 

There  are  two  methods  of  overcoming  this  difficulty: 
The  older  arrangement  consists  in  heating  the  air  by  means  of  a 
primary  coil  at  or  near  the  fan,  to  about  60  degrees,  or  to  the  minimum 
temperature  required  within  the  building.  From  the  coil  it  passes 
to  the  bases  of  the  various  flues,  and  is  there  still  further  heated  as 
required,  by  secondary  or  supplementary  heaters  placed  at  the  base  of 
each  flue. 


379 


184 


HEATING  AND  VENTILATION 


With  the  second  and  more  recent  method,  a  single  heater  is 
employed,  and  all  the  air  is  heated  to  the  maximum  required  to 
maintain  the  desired  temperature  in  the  most  exposed  rooms,  while 
the  temperature  of  the  other  rooms  is  regulated  by  mixing  with  the 
hot  air  a  sufficient  volume  of  cold  air  at  the  bases  of  the  different  flues. 
This  result  is  best  accomplished  by  designing  a  hot-blast  apparatus 

so  that  the  air  shall  be 
forced,  rather  than  drawn 
through  the  heater,  and 
by  providing  a  by-pass 
through  which  it  may 
be  discharged  without 
passing  across  the  heated 
pipes. 

The  passage  for  the 
cool  air  is  usually  above 
and  separate  from  the 
heater  pipes,  as  shown  in 
Fig.  160.  Extending 
from  the  apparatus  is  a 
double  system  of  ducts, 
usually  of  galvanized 
iron,  suspended  from  the 
ceiling.  At  the  base  of 
each  fine  is  placed  a  mix- 
ing damper,  which  is 
controlled  by  a  chain 
from  the  room  above, 
and  so  designed  as  to 
admit  either  a  full  vol- 


Fig.  161. 


Mixing  Damper  for  Regulating  Temperature      1lrnp     of 
of  Air  Supplied  by  Double  Duct  System. 


pjr      n     f,,]l 
all>     a    ] 

volume    of    cool    or 

tempered  air,  or  to  mix  them  in  any  desired  proportion  without  affect- 
ing the  resulting  total  volume  delivered  to  the  room.     A  damper  o 
this  form  is  shown  in  Fig.  161. 

Fig.  162  shows  an  arrangement  of  disc  fan  and  heater  where  the 
air  is  first  drawn  through  a  tempering  coil,  then  a  portion  of  it  forced 
through  a  second  heater  and  into  the  warm-air  pipes,  while  the  remain- 


380 


HEATING  AND  VENTILATION 


185 


dor  is  by-passed  under  the  heater  into  the  cold-air  pipes.     Mixing 


dampers  are  placed  at  the  bases  of  the  flues  as  already  described,  to 
regulate  the  temperature  in  different  rooms. 


381 


1S6  HEATING  AND  VENTILATION 


ELECTRIC  HEATING 

Unless  electricity  is  produced  at  a  very  low  cost,  it  is  not  com- 
mercially practicable  for  heating  residences  or  large  buildings.  The 
electric  heater,  however,  has  quite  a  wide  field  of  application  in  heating 
small  offices,  bathrooms,  electric  cars,  etc.  It  is  a  convenient  method 
of  warming  rooms  on  cold  mornings  in  late  spring  and  early  fall, 
when  furnace  or  steam  heat  is  not  at  hand.  It  has  the  special  advan- 
tage of  being  instantly  available,  and  the  amount  of  heat  can  be  regu- 
lated at  will.  The  heaters  are  perfectly  clean,  do  not  vitiate  the  air, 
and  are  portable. 

Electric  Heat  and  Energy.  The  commercial  unit  for  electricity 
is  one  watt  for  one  hour,  and  is  equal  to  3.41  B.  T.  V.  Electricity  is^ 
usually  sold  on  the  basis  of  1,000  watt-hours  (called  Kilowatt-hours), 


Fig.  163.    Electric  Car-Heater. 

which  is  equivalent  to  3,410  B.  T.  V.  A  watt  is  the  product  obtained 
by  multiplying  a  current  of  1  ampere  by  an  electromotive  force  of  1 
volt. 

From  the  above  we  see  that  the  B.  T.  U.  required  per  hour  for 
warming,  divided  by  3,410,  will  give  the  kilowatt-hours  necessary  for 
supplying  the  required  amount  of  heat. 

Construction  of  Electric  Heaters.  Heat  is  obtained  from  the 
electric  current  by  placing  a  greater  or  less  resistance  in  its  path. 
Various  forms  of  heaters  have  been  employed.  Some  of  the  simplest 
consist  merely  of  coils  or  loops  of  iron  wire,  arranged  in  parallel  rows, 
so  that  the  current  can  be  passed  through  as  many  coils  as  are  needed 
to  provide  the  required  amount  of  heat.  In  other  forms,  the  heating 
material  is  surrounded  with  fire-clay,  enamel,  or  asbestos,  and  in  some 
cases  the  material  itself  has  been  such  as  to  give  considerable  resist- 
ance to  the  current.  A  form  of  electric  car-heater  is  shown  in  Fig.  163. 
Forms  of  radiators  are  shown  in  Figs.  164  and  165. 


382 


HEATING  AND  VENTILATION 


187 


Calculation  of  Electric  Heaters.    The  formula  for  the  calcu- 
lation of  electric  heaters  is 

H  -P  Rt  x  .24,  . 

in  which 

H  =  Heat,  in  calorics; 
7  =  Current,  in  amperes; 
R  =  Resistance,  in  ohms; 
t  =  Time,  in  seconds. 
Examples.     What  resistance  must    an 
electric  heater   have,  to  give  off  6,000  B. 
T.  U.  per  hour,  with  a  current  of  20  am- 
peres ?  Fig.  164.    Electric  Radiator. 

We  have  learned  that  1  B.  T.  U.   =   252  calories;  so,  in  the 
present  case,  6,000  X   252  =  1,512,000  calories  must  be  provided. 
Substituting  the  known  values  in  the  formula,  we  have 

1,512,000  =  20-'  X  R  X  3,600  X  .24, 
from  which 

1,512,000 

*  = -34^600    =4-3'°hmS- 

A  heater  having  a  resistance  of  3  ohms  is  to  supply  3,000  B.  T.  U.  per 
hour.     What  current  will  be  required  ? 


Fig.  165.    Another  Form  of  Electric  Radiator. 

3,000  X  252  -  756,000  calories.     Substituting  the  known  values  in 
the  formula,  and  solving  for  I,  we  have 

756,000  =  P  X  3  X  3,600  X  .24, 
from  which 

/  =  I/  29L6  =17  +  amperes. 

Connections  for  Electric  Heaters.  The  method  of  wiring  for 
electric  heaters  is  essentially  the  same  as  for  lights  which  require  tin- 
same  amount  of  current.  A  constant  electromotive  force  or  voltage 


383 


188  HEATING  AND  VENTILATION 


is  maintained  in  the  main  wire  leading  to  the  heaters.  A  much  less 
voltage  is  carried  on  the  return  wire,  and  the  current  in  passing  through 
the  heater  from  the  main  to  the  return,  drops  in  voltage  or  pressure. 
This  drop  provides  the  energy  which  is  transformed  into  heat. 

The  principle  of  electric  heating  is  much  the  same  as  that  in- 
volved in  the  non-gravity  return  system  of- steam  heating.  In  that 
system,  the  pressure  on  the  main  steam  pipes  is  that  of  the  boiler, 
while  that  on  the  return  is  much  less,  the  reduction  in  pressure  occur- 
ring in  the  passage  of  the  steam  through  the  radiators;  the  water  of 
condensation  is  received  into  a  tank,  and  returned  to  the  boiler  by  a 
pump. 

In  a  system  of  electric  heating,  the  main  wires  must  be  suffi- 
ciently large  to  prevent  a  sensible  reduction  in  voltage  or  pressure 
between  the  generator  and  the  heater,  so  that  the  pressure  in  them 
shall  be  substantially  that  in  the  generator.  The  pressure  or  voltage 
in  the  main  return  wire  is  also  constant,  but  very  low,  and  the  genera- 
tor has  an  office  similar  to  that  of  the  steam  pump  in  the  system  just 
described — that  is,  of  raising  the  pressure  of  the  return  current  up 
to  that  in  the  main.  The  power  supplied  to  the  generator  can  be 
considered  the  same  as  the  boiler  in  the  first  case.  All  the  current 
which  passes  from  the  main  to  the  return  must  flow  through  the  heater, 
and  in  so  doing  its  pressure  or  voltage  falls  from  that  of  the  main 
to  that  of  the  return. 

From  the  generator  shown  in  Fig.  166,  main  and  return  wires 
are  run  the  same  as  in  a  two-pipe  system  of  steam  heating,  and  these 
are  proportioned  to  carry  the  required  current  without  sensible  drop 
or  loss  of  pressure.  Between  these  wires  are  placed  the  various 
heaters,  which  are  arranged  so  that  when  electric  connection  is  made 
they  draw  the  current  from  the  main  and  discharge  it  into  the  return 
wire.  Connections  are  made  and  broken  by  switches,  which  take  the 
place  of  valves  on  steam  radiators. 

Cost  of  Electric  Heating.  The  expense  of  electric  heating  must 
in  every  case  be  great,  unless  the  electricity  can  be  supplied  at  an 
exceedingly  low  cost.  Estimated  on  the  basis  of  present  practice, 
the  average  transformation  into  electricity  does  not  account  for  more 
than  4  per  cent  of  the  energy  in  the  fuel  which  is  burned  in  the  furnace. 
Although  under  best  conditions  15  per  cent  has  been  realized,  it 
would  not  be  safe  to  assume  that  in  ordinary  practice  more  than  5 


384 


HEATING  AND  VENTILATION 


1S9 


per  cent  could  be  transformed  into  electrical  energy.  In  heating 
with  steam,  hot  water,  or  hot  air,  the  average  amount  utilized  will 
probably  be  about  60  per  cent,  so  that  the  expense  of  electrical  heating 
is  approximately  from  12  to  15  times  greater  than  by  these  methods. 

TEMPERATURE   REGULATORS 

The  principal  systems  of  automatic  temperature  control  now  in 
use,-  consist  of  three  essential  features;  First,  an  air-compressor, 
reservoir,  and  distributing  pipes;  second,  thermostats,  which  are 


Fig.  166.    General  System  of  Wiring  a  House  for  Electric  Heating. 

placed  in  the  rooms  to  be  regulated;  and  third,  special  diaphragm  or 
pneumatic  valves  at  the  radiators. 

The  air-compressor  is  usually  operated  by  water-pressure  in 
small  plants  and  by  steam  in  larger  ones;  electricity  is  used  in  some 
cases.  Fig.  167  shows  a  form  of  water  compressor.  It  is  similar 
hi  principle  to  a  direct-acting  steam  pump,  in  which  water  under 
pressure  takes  the  place  of  steam.  A  piston  in  the  upper  cylinder 
compresses  the  air,  which  is  stored  in  a  reservoir  provided  for  the 
purpose.  When  the  pressure  in  the  reservoir  drops  below  a  certain 


385 


190 


HEATING  AND  VENTILATION 


point,   the  compressor  is  started  automatically,   and   continues  to 
operate  until  the  pressure  is  brought  up  to  its  working  standard. 

A  ihermostat  is  simply  a  mechanism  for  opening  and  closing 
one  or  more  small  valves,  and  is  actuated  by  changes  in  the  tempera- 


ig.  It".  Air-Compressor  Operated  by  Wa- 
ter-Pressure. Automatically  Controlled, 
and  Operating  to  Regulate  Temperature 
by  Controlling:  Radiator  Valves. 


Fig.  168.  Thermostat  Controlling  Valves 
on  Radiators,  and  Operating  through  Ex- 
pansion or  Contraction  of  Metal  Strip  E. 


ture  of  the  air  in  which  it  is  placed.  Fig.  168  shows  a  thermostat 
in  which  the  valves  are  operated  by  the  expansion  and  contraction 
of  the  metal  strip  E.  The  degree  of  temperature  at  which  it  acts 
may  be  adjusted  by  throwing  the  pointer  at  the  bottom  one  way  or 
the  other.  Fig.  1G9  shows  the  same  thermostat  with  its  ornamental 


386 


HEATING  AND  VENTILATION 


191 


casing  in  place.  The  thermostat  shown  in  Fig.  170  operates  on 
a  somewhat  different  principle.  It  consists  of  a  vessel  separated  into 
two  chambers  by  a  metal  diaphragm. 
One  of  these  chambers  is  partially 
filled  with  a  liquid  which  will  boil 
at  a  temperature  beiow  that  desired 
in  the  room.  The  vapor  of  the 
liquid  'produces  considerable  pres- 
sure at  the  normal  temperature  of 
the  room,  and  a  slight  increase  of 
heat  crowds  the  diaphragm  over 
and  operates  the  small  valves  in  a 
manner  similar  to  that  of  the  metal 
strip  in  the  case  just  'described. 

The  general  form  of  a  dia- 
phragm valve  is  shown  in  Fig.  171. 
These  replace  the  usual  hand-valves 
at  the  radiators.  They  are  similar 
in  construction  to  the  ordinary 
globe  or  angle  valve,  except  that 
the  stem  slides  up  and  down  in- 
stead of  being  threaded  and  run- 
ning in  a  nut.  The  top  of  the  stem 
connects  with  a  flat  plate,  which 
rests  against  a  rubber  diaphragm. 
The  valve  is  held  open  by  a  spring, 
as  shown,  and  is  closed  by  admit- 
ting compressed  air  to  the  space 
above  the  diaphragm. 

In  connecting  up  the  system, 
small  concealed  pipes  are  carried 
from  the  air-reservoir  to  the  ther- 
mostat, which  is  placed  upon  an 
inside  wall  of  the  room,  and  from 
there  to  the  diaphragm  valve  at 
the  radiator.  When  the  temperature  of  the  room  reaches  the  maxi- 
mum point  for  which  the  thermostat  is  set,  its  action  opens  a  small 
valve  and  admits  air-pressure  to  the  diaphragm,  thus  closing  off  the 


Fig.  169.    Thermostat  of  Fig.  168  in 
Ornamental  Casing. 


387 


102 


HEATING  AND  VENTILATION 


steam  from  the  radiator.  When  the  temperature  falls,  the  thermostat 
acts  in  the  opposite  manner,,  and  shuts  off  the  air-pressure  from  the 
diaphragm  valve,  at  the  same  time  opening  a  small  exhaust  which 
allows  the  air  above  the  diaphragm  to  escape.  The  pressure  being 
removed,  the  valve  opens  and  again  admits  steam  to  the  radiator. 

Diaphragm  Motors.  Dampers  are  operated  pneumatically  in 
a  similar  manner  to  steam  valves.  A  diaphragm  motor,  so  called,  is 
acted  upon  by  the  air-pressure;  and  this  lifts  a  lever  which  is  properly 
connected  to  the  damper  by  means  of  chains  or  levers,  thus  securing 
the  desired  movement. 

Dampers.  When  mixing-  dampers  are  operated  pneumatically, 
a  specially  designed  thermostat  for  giving  a  graduated  movement 


at  Opcrat 


if*  through  Expansion  or  Contraction  of  the  Vapor 
of  a  Volatile  Liquid. 


(o  the  damper  should  be  used.  By  this  arrangement  the  damper 
is  held  in  such  a  position  at  all  times  as  to  admit  the  proper  proportions 
of  hot  and  cold  or  tempered  air  for  producing  the  desired  temperature 
in  the  room  with  which  it  is  connected. 

Large  dampers  which  are  to  be  operated  pneumatically,  should 
be  made  up  in  sections  or  louvres.  Dampers  constructed  in  this 
manner  are  handled  much  more  easily  than  when  made  in  a  single 
piece. 

It  often  happens,  in  large  plants,  that  there  are  valves,  and 
dampers  in  places  which  are  not  easily  reached  for  hand  manipula- 
tion. These  may  be  provided  with  diaphragms  and  connected  with 
the  air-pressure  system  for  operation  by  hand-switches  or  cocks 


338 


HEATING  AND  VENTILATION 


19S 


conveniently  located  at  some  centra/  point  in  the  basement  or  boiler 
room. 

Telethermometer.  This  is  a  device  for  indicating  on  a  dial 
at  some  central  point  the  temperature  of  various  rooms  or  ducts  in 
different  parts  of  a  building.  A  special  transmitter  is  placed  in  each 
of  the  rooms  and  electrically  connected  with  a  central  switchboard. 
Then,  by  means  of  suitable  switches,  any  room  may  be  thrown  in 
circuit  with  the  recorder,  and  the  temperature  existing  in  the  room 
at  that  time  read  from  the  dial. 


Fig.  171.    Exterior  View,  and  Section  Showing  Interior  Mechanism  of  Diaphragm  Valve. 

.Humidostat.  The  kumidostat  is  a  device  to  be  placed  in  one  or 
more  rooms  of  a  building  for  maintaining  an  even  percentage  of 
moisture  in  the  air.  The  apparatus  consists  of  two  essential  parts — 
the  humidostat  and  the  humidifier.  The  former  corresponds,  to  the 
thermostat  in  a  system  of  temperature  control,  and  operates  a  pneu- 
matic valve  or  other  mechanism  connected  with  the  humidifier  when 
the  percentage  of  moisture  rises  above  or  falls  below  certain  limits. 
The  operating  medium  is  compressed  air,  the  same  as  for  tempera- 
ture control;  and  the  two  devices  are  usually  connected  with  the  same 
pressure  system. 


389 


194  HEATING  AND  VENTILATION 

The  normal  moisture  of  a  room  is  70  per  cent,  and  should  never 
exceed  that.  In  cold  weather  it  will  be  necessary  to  reduce  the 
amount  of  moisture  somewhat,  owing  to  the  "sweating"  of  walls  and 
windows. 

The  method  of  moistening  the  air  will  depend  somewhat  upon 
circumstances.  If  the  air  for  ventilation  is  delivered  to  the  rooms  at 
a  temperature  not  exceeding  70  degrees,  the  humidifier  is  best  placed 
in  the  main  air-duct.  '  If  the  air  enters  at  a  higher  temperature,  the 
humidifier  must  be  located  in  the  same  room  with  the  humidostat. 

The  moistener  or  humidifier  may  be  of  any  one  of  several  forms. 
"NVhere  steam  heating  is  used,  and  where  the  steam  is  clean  and  odor- 
less and  free  from  oil  from  engines,  a  perforated  pipe  (or  pipes)  in  the 
air-duct  is  the  simplest  and  best  humidifier.  The  outlets  are  properly 
adjusted,  and  then  the  humidostat  shuts  off  and  lets  on  the  steam 
as  required.  Sometimes  a  water  spray,  particularly  of  warm  water, 
may  be  used  in  place  of  steam.  "Wnen  neither  steam  jet  nor  water 
spray  is  advisable,  an  evaporating  pan  containing  a  steam  coil  may 
be  used,  the  humidostat  controlling  the  steam  to  the  coil,  and  the 
water-level  in  the  pan  being  kept  constant  by  means  of  a. ball-cock. 

AIR=FILTERS  AND  AIR=WASHERS 

In  cases  where  the  air  for  ventilating  purposes  is  likely  to  contain 
soot  or  street  dust,  it  is  desirable  to  provide  some  form  of  filter  for 
purifying  it  before  delivering  to  the  rooms.  If  the  air-quantity  is 
small  and  there  is  plenty  of  room  between  the  inlet  windows  and 
the  fan,  screens  of  light  cheesecloth  may  be  used  for  this  purpose. 
The  cloth  should  be  tacked  to  light  but  substantial  wooden  frames, 
which  can  be  easily  removed  for  frequent  cleaning.  These  screens  are 
usually  set  up  in  "saw-tooth"  fashion  in  order  to  give  as  much  sur- 
face as  possible  in  the  least  space. 

Another  arrangement,  used  in  case  of  large  volumes  of  air, 
is  to  provide  a  number  of  light  cloth  bags  of  considerable  length, 
through  which  the  air  is  drawn  before  reaching  the  heater.  These  are 
fastened  to  a  suitable  frame  or  partition  for  holding  them  open.  The 
great  objection  to  filters  of  this  kind  is  their  obstruction  to  the  passage 
of  the  air,  especially  wjien  filled  with  dust,  the  frequent  intervals  at 
which  they  should  be  cleaned,  and  the  great  amount  of  filtering  sur- 
face required. 


390 


HKATING  AND  VENTILATION 


195 


An  apparatus  which  is 
coming  quite  generally  into 
use  for  this  purpose,  and  ' 
which  does  away  with  the 
disadvantages  noted  above, 
is  the  spray  filter  or  air- 
washer,  one  form  of  which 
is  shown  in  Fig.  172.  Air 
enters  as  indicated,  and 
first  passes  through  a  tem- 
pering coil  to  raise  it  above 
the  freezing  point  in  win- 
ter weather;  then  passes 
through  the  spray-chamber, 
where  the  dirt  is  removed; 
then  through  an  eliminator 
for  removing  the  water; 
and  then  through  a  second 
heater  on  -its  way  to  the 
fan. 

The  water  is  forced 
through  the  spray-heads 
by  means  of  a  small  cen- 
trifugal pump;  either  belted 
to  the  fan  shaft  or  driven 
by  an  independent  motor. 

HEATING  AND 
VENTILATION  OF 
VARIOUS  CLASSES 
OF  BUILDINGS 

The  different  methods 
used  in  heating  and  venti- 
lation, together  with  the 
manner  of  computing  the 
various  proportions  of  the 
apparatus,  having  been 


391 


196  HEATING  ANT)  VENTILATION 


taken  up,  the  application  of  these  systems  to  the  different  classes 
<;f  buildings  will  now  be  considered  briefly. 

School  Buildings.  For  school  buildings  of  small  size,  the  furnace 
system  is  simple,  convenient,  and  generally  effective.  Its  use  is  con- 
fined as  a  general  rule  to  buildings  having  not  more  than  six  or  eight 
rooms.  For  large  ones  this  method  must  generally  give  way  to  some 
form  of  indirect  steam  system  with  one  or  more  boilers,  which  occupy 
less  space,  and  are  more  easily  cared  for  than  a  number  of  furnaces 
scattered  about  in  different  parts  of  the  basement.  As  in  all  systems 
that  depend  on  natural  circulation,  the  supply  and  removal  of  air  is 
considerably  affected  by  changes  in  the  outside  temperature  and  by 
winds. 

The  furnaces  used  are  generallv  built  of  cast  iron,  this  material 
being  durable,  and  easily  made  to  present  large  and  effective  heating 
surfaces.  To  adapt  the  larger  sizes  of  house-heating  furnaces  to 
schools,  a  much  larger  space  must  be  provided  between  the  body  and 
the  casing,  to  permit  a  sufficient  volume  of  air  to  pass  to  the  rooms. 
The  free  area  of  the  air-passage  should  be  sufficient  to  allow  a  velocity 
of  about  400  feet  per  minute. 

The  size  of  furnace  is  based  on  the  amount  of  heat  lost  by  radia- 
tion and  conduction  through  "walls  and  windows,  phis  that  carried 
away  by  air  passing  up  the  ventilating  flues.  These  quantities  may 
be  computed  by  the  usual  methods  for  "loss  of  heat  by  conduction 
through  walls,"  and  "heat  required  for  ventilation."  With  more 
regular  and  skilful  attendance,  it  is  safe  to  assume  a  higher  rate  of 
combustion  in  schoolhouse  heaters  than  in  those  used  for  warming 
residences.  Allowing  a  maximum  combustion  of  G  pounds  of  coal 
per  hour  per  square  foot  of  grate,  and  assuming  that  8,000  B.  T.  U. 
per  pound  are  taken  up  by  the  air  passing  over  the  furnace,  we  have 
6  X  8,000  =  48,000  B.  T.  U.  furnished  per  hour  per  square  foot  of 
grate.  Therefore,  if  we  divide  the  total  B.  T.  U.  required  for  both 
warming  and  ventilation  by  48,000,  it  will  give  us  the  necessary  grate 
surface  in  square  feet.  It  has  been  found  in  practice  that  a  furnace 
with  a  firepot  32  inches  in  diameter,  and  having  ample  heating  surface, 
is  capable  of  heating  two  50-pupil  rooms  in  zero  weather.  The  sizes 
of  ducts  and  flues  may  be  determined  by  rules  already  given  under 
furnace  and  indirect  steam  heating. 

The  velocity  of  the  warm  air  within  the  uptake  flues  depends 


392 


HEATING  AND  VENTILATION  19? 


Upon  their  height  and  the  difference  in  temperature  between  the 
warm  air  within  the  flues  and  the  cold  air  outside.  The  action  of 
the  wind  also  affects  the  velocity  of  air-flow.  It  has  been  found  by 
experience  that  flues  having  sectional  areas  of  about  6  square  feet  for 
first-floor  rooms,  5  square  feet  for  the  second  floor,  and  4\  square  feet 
for  the  third,  will  be  of  ample  size  for  standard  classrooms  seating 
from  40  to  50  pupils  in  primary  and  grammar  schools.  These  sizes 
may  be  used  for  both  furnace  and  indirect  gravity  steam  heating. 

The  vent  flues  may  be  made  5  square  feet  for  the  first  floor,  and 
6  square  feet  for  the  second  and  third  floors.  They  may  be  ar- 
ranged in  banks,  and  carried  through  the  roof  in  the  form  of  large 
chimneys,  or  may  be  carried  to  the  attic  space  and  there  gathered 
by  means  of  galvanized-iron  ducts  connecting  with  roof  vents  of 
wood  or  copper  construction. 

In  order  to  make  the  vent  flues  "draw"  sufficiently  in  mild  or 
heavy  weather,  it  is  necessary  to  provide  some  means  for  warming 
the  air  within  them  to  a  temperature  somewhat  above  that  of  the 
rooms  with  which  they  connect.  This  may  be  done  by  placing  a 
small  stove  made  specially  for  the  purpose,  at  the  base  of  each  flue. 
If  this  is  done,  it  is  necessary  to  carry  the  air  down  and  connect  with 
the  flue  just  below  the  stove. 

The  cold-air  supply  duct  to  each  furnace  should  be  made  f 
the  size  of  all  the  warm-air  flues  if  free  from  bends,  or  the  full 
size  if  obstructed  in  any  way. 

The  inlet  and  outlet  openings  from  the  rooms  into  the  flues,  are 
commonly  provided  with  grilles  of  iron  wire  having  a  mesh  of  2  to  2  j 
inches.  Both  flat  and  square  wire  are  used  for  this  purpose.  Mixing 
dampers  for  regulating  the  temperature  of  the  rooms  should  be  pro- 
vided for  each  flue.  The  effectiveness  of  these  dampers  will  depend 
largely  upon  their  construction;  and  they  should  be  made  tight 
against  cold-air  leakage,  by  covering  the  surfaces  or  flanges  against 
which  they  close  with  some  form  of  asbestos  felting.  Both  inlet  and 
outlet  gratings  should  be  provided  with  adjustable  dampers.  One  of 
the  disadvantages  of  this  system  is  the  delivery  of  all  the  heat  to  the 
room  from  a  single  point,  and  this  not  always  in  a  position  to  give  the 
best  results.  The  outer  walls  are  thus  left  unwarmed,  except  as  the 
heat  is  diffused  throughout  the  room  by  air-currents.  When  there  is 
considerable  glass  surface,  as  in  most  of  our  modern  schoolrooms, 


393 


108  HEATING  AND  VENTILATION 


draughts  and  currents  of  cold  air  arc  frequently  found  along  the  out- 
side walls. 

The  indirect  gravity  system  of  steam  heating  comes  next  in  cost 
of  installation.  Qnc  important  advantage  of  this  system  over  furnace 
heating  comes  from  the  ability  to  place  the  heating  coils  at  the  base 
of  the  flues,  thus  doing  away  with  horizontal  runs  of  air-pipe,  which 
are  required  to  some  extent  in  furnace  heating.  The  warm-air 
currents  in  the  flues  are  less  affected  by  variations  in  the  direction  and 
force  of  the  wind  where  this  construction  is  possible,  and  this  is  of 
much  importance  in  exposed  locations. 

The  method  of  supplying  cold  air  to  the  coils  or  heaters  is  im- 
portant, and  should  be  carefully  worked  out.  The  supply  should  be 
taken  from  at  least  two  sides  of  the  building,  or,  if  possible,  from  all 
four  sides.  When  it  is  taken  from  four  sides,  each  inlet  should  be 
made  large  enough  to  supply  one-half  the  amount,  or,  in  other  words, 
any  two  should  give  the  total  quantity  required.  It  is  often  possible 
to  arrange  the  flues  in  groups  so  that  all  the  heating  stacks  may  be 
placed  in  two  or  more  cold-air  chambers,  depending  upon  the  size 
of  the  building.  A  cold-air  trunk  line  may  be  run  through  the  center 
of  the  basement,  connecting  with  the  outside  on  all  four  sides,  and 
having  branches  supplying  each  cold-air  chamber. 

Cast-iron  pin-radiators  are  particularly  adapted  to  this  class 
of  work. 

The  School-Pin,  having  a  section  about  10  inches  in  depth  and 
rated  at  15  square  feet  of  heating  surface  per  section,  is  used  quite 
extensively  for  this  purpose.  Stacks  containing  about  240  square 
feet  of  surface  for  southerly  rooms,  and  260  for  those  having  a  north- 
erly exposure,  have  been  found  ample  for  ordinary  conditions  in  zero 
weather. 

A  very  satisfactory  arrangement  is  the  use  of  indirect  heaters 
for  warming  the  air  needed  for  ventilation,  and  the  placing  of  direct 
radiation  in  the  rooms  for  heating  purposes.  The  general  construc- 
tion of  the  indirect  stacks  and  flues  may  be  the  same;  but  the  heating 
surface  can  be  reduced,  as  the  air  in  this  case  must  be  raised  only  to 
70  or  75  degrees  in  zero  weather,  the  heat  to  offset  that  lost  by  con- 
duction, etc.,  through  walls  and  windows  being  provided  by  the 
direct  surface.  The  mixing  dampers  may  be  omitted,  and  the  tem- 
perature of  the  room  regulated  by  opening  or  closing  the  steam  valves 


394 


DIRECT-INDIRECT  METHOD  OF  WARMING  TAKING  A  FRESH  AIR  SUPPLY 
FROM  OUTSIDE  AND  PASSING  IT  UPWARD 

American  Kadiator  Company 


HEATING  AND  VENTILATION  199 

on  the  direct  coils,  which  should  be  done  automatically.  The  direct- 
heating  surface,  which  is  best  made  up  of  lines  of  lj-inch  pipe,  should 
be  placed  along  the  outer  walls  beneath  the  windows  This  supplies 
heat  where  most  needed,  and  does  away  with  the  tendency  to  draughts. 
In  mild  weather,  during  the  spring  and  fall,  the  indirect  heaters  may 
prove  sufficient  for  both  ventilation  and  warming. 

Where  direct  radiation  is  placed  in  the  rooms,  the  quantity  of 
heat  supplied  is  not  affected  by  varying  wind  conditions,  as  is  the 
case  in  indirect  heating.  Although  the  air-supply  may  be  reduced 
at  times,  the  heat  quantity  is  not  changed.  Direct  radiation  has  the 
disadvantage  of  a  more  or  less  unsightly  appearance,  and  architects 
and  owners  often  object  to  the  running  of  mains  or  risers  through 
the  rooms  of  the  building.  Air-valves  should  always  be  provided 
with  drip  connections  carried  to  a  sink  or  dry  well  in  the  basement. 

When  circulation  coils  are  used,  a  good  method  of  drainage  is 
to  carry  separate  returns  from  each  coil  to  the  basement,  and  to  place 
the  air-valves  in  the  drops  just  below  the  basement  ceiling.  A  check- 
valve  should  be  placed  below  the  wrater-line  in  each  return. 

The  gravity  system  has  the  fault  of  not  supplying  a  uniform 
quantity  of  air  under  all  conditions  of  outside  temperature,  the  same 
as  a  furnace,  but  when  properly  arranged,  may  be  made  to  give  quite 
satisfactory  results. 

The  fan  or  blower  system  for  ventilation,  writh  direct  radiation 
in  the  rooms  for  warming,  is  considered  to  be  one  of  the  best  possible 
arrangements. 

In  designing  a  plant  of  this  kind,  the  main  heating  coil  should 
be  of  sufficient  size  to  warm  the  total  air-supply  to  70  or  75  degrees 
in  the  coldest  weather,  and  the  direct  surface  should  be  proportioned 
for  heating  the  building  independently  of  the  indirect  system.  Auto- 
matic temperature  regulation  should  be  used  in  connection  with 
systems  of  this  kind,  by  placing  pneumatic  valves  on  the  direct  radia- 
tion. It  is  customary  to  carry  from  3  to  8  pounds  pressure  on  the 
direct  system,  and  from  8  to  15  pounds  on  the  main  coil,  depending 
upon  the  outside  temperature.  The  foot-warmers,  vestibule,  and 
office  heaters  should  be  placed  on  a  separate  line  of  piping,  with 
separate  returns  and  trap,  so  that  they  can  be  used  independently 
of  the  rest  of  the  building  jf  desired.  Where  there  is  a  large  assembly 
hall,  it  should  be  arranged  so  that  it  can  be  both  wanned  and  venti- 


395 


200  HEATING  AND  VENTILATION 


lated  when  the  rest  of  the  building  is  shut  off.  This  can  be  done  by  a 
proper  arrangement  of  valves  and  dampers. 

When  different  parts  of  the  system  are  run  on  different  pressures, 
the  returns  from  each  should  discharge  through  separate  traps  into 
a  receiver  having  connection  with  the  atmosphere  by  means  of  a  vent 
pipe.  Fig.  173  shows  a  common  arrangement  for  the  return  con- 
nections in  a  combination  system  of  this  kind.  The  different  traps 
discharge  into  the  vented  receiver  as  shown;  and  the  water  is  pumped 
back  to  the  boiler  automatically  when  it  rises  above  a  given  level  in 
the  receiver,  a  pump  governor  being  used  to  start  and  stop  the  pumps 
as  required. 

A  water-level  or  seal  of  suitable  height  is  maintained  in  the  main 
returns,  by  placing  the  trap  at  the  required  elevation  and  bringing 
the  returns  into  it  near  the  bottom ;  a  balance  pipe  is  connected  with 
the  top  for  equalizing  the  pressure,  the  same  as  in  the  case  of  a  pump 
governor.  .Sometimes  a  fan  is  used  with  the  heating  coils  placed  at 
the  base  of  the  flues,  instead  of  in  the  rooms.  Where  this  is  done 
the  radiating  surface  may  be  reduced  about  one-half.  This  system 
is  less  expensive  to  install,  but  has  the  disadvantage  of  removing  the 
heating  surface  from  the  cold  walls,  where  it  is  most  needed. 

With  a  blower  type  of  fan,  the  size  of  the  main  ducts  may  be 
based  on  a  velocity  of  from  1,000  to  1,200  feet  per  minute,  and  the 
branches  on  a  velocity  of  800  to  1 ,000  feet  per  minute. 

The  velocity  in  the  vertical  flues  may  be  from  (iOO  to  TOO  feet  per 
minute,  although  the  lower  velocity  is  preferable. 

The  size  of  the  inlet  registers  should  be  such  that  the  velocity 
of  the  entering  air  will  not  exceed  350  to  400  feet  per  minute. 

When  the  air  is  delivered  through  a  register  at  the  high  velocities 
mentioned,  some  means  must  be  provided  for  diffusing  the  entering 
current,  in  order  to  prevent  disagreeable  draughts.  This  is  usually 
accomplished  by  the  use  of  deflecting  blades  of  galvanized  iron,  set 
in  a  vertical  position  and  at  varying  angles,  so  that  the  air  is  thrown 
towards  each  side  as  it  issues  from  the  register.  The  size  of  the 
vent  flues  should  be  about  the  same  as  for  a  gravity  system — that  is, 
about  6  square  feet  for  a  standard  classroom,  and  in  the  same  pro- 
portion for  smaller  rooms. 

Vent-flue  heaters  are  not  usually  required  in  connection  with  a 
fan  system,  as  the  force  of  the  fan  is  sufficient  to  supply  the  required 


396 


HEATING  AND  VENTILATION 


201 


397 


202  HEATING  AXI)  VENTILATION 


quantity  of  air  at  all  times  \vithout  the  aspirating  effect  of  the  vent 
flues. 

The  method  of  piping  shown  in  Fig.  173  applies  especially  to 
buildings  of  large  size.  In  the  case  of  medium-sized  buildings,  it 
is  often  possible  to  use  pin  radiation  for  the  main  heater,  placing  the 
same  well  above  the  water-line  of  the  boilers  and  thus  returning  the 
condensation  by  gravity,  without  the  use  of  pumps  or  traps.  When 
this  arrangement  is  used,  an  engine  with  a  large  cylinder  should  be 
employed,  so  that  the  steam  pressure  will  not  exceed  15  or  1«S  pounds, 
and  the  whole  system,  including  the  direct  surface,  may  be  run  upon 
the  same  system. 

This  is  a  very  simple  arrangement,  and  is  adapted  to  all  build- 
ings of  small  and  medium  size  where  the  heater  can  be  placed  at  a 
sufficient  height  above  the  boilers. 

Temperature  control  is  usually  secured  automatically  by  placing 
pneumatic  valves  upon  either  the  direct  or  supplementary  heaters. 
Mixing  dampers  are  sometimes  used  instead,  in  the  latter  case.  Every 
fan  system  should  be  provided  with  a  thermometer  of  large  size  for 
indicating  the  temperature  of  the  air  in  the  main  duct  just  beyond 
the  fan. 

The  ventilation  of  the  toilet-rooms  of  a  school  building  is  a 
matter  of  the  greatest  importance.  The  first  requirement  is  that  the 
air-movement  shall  be  into  these  rooms  from  the  corridors  instead  of 
outward.  To  obtain  this  result,  it  is  necessary  to  produce  a  slight 
vacuum  within,  and  this  cannot  well  be  done  if  fresh  air  is  forced 
into  them. 

One  of  the  most  satisfactory  arrangements  is  to  provide  exhaust 
ventilation  only,  and  to  remove  the  greater  part  of  the  air  through 
local  vents  connecting  with  the  fixtures.  *• 

Hospitals.  The  best  system  for  heating  and  ventilating  a  hos- 
pital depends  upon  the  character  and  arrangement  of  the  buildings. 
It  is  desirable  in  all  cases  to  do  the  heating  from  a  central  plant, 
rather  than  to  carry  fires  in  the  separate  buildings,  both  on  account 
of  economy  and  for  cleanliness. 

In  the  case  of  small  cottage  hospitals  with  two  or  three  buildings 
placed  close  together,  indirect  hot  water  affords  a  desirable  system  for 
the  wards,  with  direct  heat  for  the  other  rooms ;  but  where  there  are 
several  buildings,  and  especially  if  they  are  some  distance  apart,  it 


398 


HEATING  AND  VENTILATION  203 

becomes  necessary  to  substitute  steam  unless  the  water  is  pumped 
through  the  mains.  For  large  city  buildings,  a  fan  system  is  always 
desirable. 

If  the  building  is  tall  compared  with  its  ground  area,  so  that 
the  horizontal  supply  ducts  will  be  comparatively  short,  the  double- 
duct  system  may  be  used  with  good  results.  Where  the  rooms  are 
of  good  size,  and  the  number  of  supply  flues  not  great,  the  use  of 
supplementary  heaters  at  the  bases  of  the  flues  makes  a  satisfactory 
arrangement.  Direct  radiation  should  never  be  used  in  the  wards 
when  it  can  be  avoided,  even  in  connection  with  an  independent  air- 
supply,  as  it  offers  too  great  an  opportunity  for  the  accumulation  of 
dust  in  places  which  are  difficult  to  reach. 

It  is  common  to  provide  from  80  to  100  cubic  feet  of  air  per 
minute  per  patient  in  ordinary  wards,  and  from  100  to  120  cubic  feet 
in  contagious  wards. 

The  usjial  ward  building  of  a  modern  cottage-hospital  generally 
contains  a  main  ward  having  from  8  to  12  beds,  and  a  number  of 
private  rooms  of  one  bed  each. 

In  addition  to  these,  there  are  a  diet  kitchen,  duty-room,  toilet- 
rooms,  bathrooms,  linen-closets,  and  lockers. 

For  moderately  sheltered  locations,  30  square  feet  of 'indirect 
steam  radiation  has  been  found  sufficient  in  zero  weather  for  a  single 
ward  with  one  exposed  wall  and  a  single  window,  when  upon  the 
south  side  of  the  building. 

For  northerly  rooms,  40  square  feet  should  be  used.  In  exposed 
locations,  the  heaters  may  be  made  40  and  50  square  feet  for  north 
and  south  rooms  respectively.  The  standard  pin-radiators  rated  at 
10  square  feet  of  heating  surface  per  section,  are  commonly  used  for 
this  purpose.  In  case  hot  water  is  used,  the  same  number  of  sections 
of  the  deep-pin  pattern  rated  at  15  square  feet  each  may  be  employed, 
making  a  total  of  45  and  60  square  feet  per  room.  For  corner  rooms 
having  two  exposed  walls  and  two  windows,  the  amount  of  radiation 
should  be  increased  about  50  per  cent  over  that  given  above. 

The  wards  are  usually  furnished  with  fireplaces  which  provide 
for  the  discharge  ventilation.  In  case  the  fireplaces  are  omitted,  a 
special  vent  flue,  either  of  brick  or  of  galvanized  iron,  should  be  pro- 
vided. These  should  not  be  less  than  8  by  12  inches  for  single  wards, 
and  the  equivalent  for  each  bed  in  a  large  ward.  Each  flue  of  this 


399 


204  HEATING  AND  VENTILATION 

kind  should  have  a  loop  of  steam  pipe  for  producing  a  draught.  A 
loop  of  1-inch  pipe,  10  or  12  feet  in  height,  is  usually  sufficient  for 
this  purpose. 

Other  rooms  than  wards  are  usually  heated  with  direct  radia- 
tors, the  sizes  of  which  may  he  computed  in  the  same  manner  as  for 
dwelling-houses. 

Steam  tables  for  the  kitchen,  sterilizers,  and  laundry  machinery, 
require  higher  pressures  than  is  necessary  for  heating. 

In  large  plants  the  boilers  are  usually  run  at  high  pressure,  and 
the  pressure  reduced  for  heating.  A  good  arrangement  for  small 
plants  is  to  provide  sufficient  boiler  power  for  warming  and  ventilating 
purposes,  and  run  at  a  pressure  of  3  to  5  pounds.  In  addition  to 
this,  a  small  high-pressure  boiler  carrying  70  or  SO  pounds  should  be 
furnished  for  laundry  work  and  water  heating. 

Churches.  Churches  may  be  warmed  by  furnaces,  by  indirect 
.steam,  or  by  means  of  a  fan.  For  small  buildings  the  furnace  is 
more  commonly  used.  This  apparatus  is  the  simplest  of  all  and  is 
comparatively  inexpensive.  Heat  may  be  generated  quickly,  and 
when  the  fires  are  no  longer  needed,  they  may  be  allowed  to  go  out 
without  danger  of  damage  to  any  part  of  the  system  from  freezing. 

It  is  not  usually  necessary  that  the  heating  apparatus  be  large 
enough  to  warm  the  entire  building  at  one  time  to  70  degrees  with 
frequent  change  of  air.  If  the  building  is  thoroughly  warmed  before 
occupancy,  either  by  rotation  or  by  a  slow  inward  movement  of 
outside  air,  the  chapel  or  Sunday-school  room  may  be  shut  off  until 
near  the  close  of  the  service  in  the  auditorium,  when  a  portion  of  the 
warm  air  may  be  turned  into  it.  When  the  service  ends,  the  switch- 
damper  is  opened  wide,  and  all  the  air  is  discharged  into  the  Sunday- 
school  room.  The  position  of  the  warm-air  registers  will  depend 
somewhat  upon  the  construction  of  the  building,  but  it  is  well  to  keep 
them  near  the  outer  walls  and  the  colder  parts  of  the  room.  Large 
inlet  registers  should  be  placed  in  the  floor  near  the  entrance  doors, 
to  stop  cold  draughts  from  blowing  up  the  aisles  when  the  doors  are 
opened,  and  also  to  be  used  as  foot-warmers. 

Ceiling  ventilators  are  generally  provided,  but  should  be  no 
larger  than  is  necessary  to  remove  the  products  of  combustion  from 
the  gaslights,  etc.  If  too  large,  much  of  the  warmest  and  purest 
air  will  escape  through  them.  The  main  vent  flues  should  be  placed 


400 


HEATING  AND  VENTILATION  205 

in  or  near  the  floor  and  should  be  connected  with  a  vent  shaft  leading 
outboard.  This  flue  should  be  provided  with  a  small  stove  or  flue 
heater  made  specially  for  this  purpose.  In  cold  weather  the  natural 
draught  will  be  found  sufficient  in  most  cases. 

The  same  general  rules  are  to  be  followed  in  the  case  of 
indirect  steam  as  have  been  described  for  furnace  heating.  The 
stacks  are  placed  beneath  the  registers  or  flues,  and  mixing  dampers 
provided.  If  there  are  large  windows,  flues  should  be  arranged  to 
open  .in  the  window-sills,  so  that  a  sheet  of  warm  air  may  be  delivered 
in  front  of  the  windows,  to  counteract  the  effects  of  cold  down-draughts 
from  the  exposed  glass.  These  flues  may  usually  be  made  3  or  4 
inches  in  depth,  and  should  extend  the  entire  width  of  the  window. 
Small  rooms,  such  as  vestibules,  library,  pastor's  room,  etc.,  are  usually 
heated  with  direct  radiators.  Rooms  which  are  used  during  the 
week  are  often  connected  with  an  independent  heater  so  that  they 
may  be  warmed  without  running  the  large  boilers,  as  would  otherwise 
be  necessary. 

When  a  fan  is  used,  it  is  desirable,  if  possible,  to  deliver  the  air 
to  the  auditorium  through  a  large  number  of  small  openings.  This 
is  often  done  by  constructing  a  shallow  box  under  each  pew,  running 
its  entire  length,  and  connecting  it  with  the  distributing  ducts  or  a 
plenum  space  by  means  of  a  pipe  from  below.  The  air  is  delivered 
at  a  low  velocity  through  a  long  slot,  as  shown  in  Fig.  174. 

The  warm-air  flues  in  the  window-sills  should  be  retained,  but 
may  be  made  shallower,  and  the  air  forced  in  at  a  high  velocity. 

If  the  auditorium  has  a  sloping  floor,  a  plenum  space  may  be 
provided  between  the  upper  or  raised  portion  and  the  main  floor. 
Sometimes  a  shallow  basement  3  or  4  feet  in  height,  with  a  cemented 
floor,  and  extending  under  the  entire  auditorium,  is  used  as  an  air 
or  plenum  space. 

If  the  basement  is  of  good  height  and  used  for  storage  or  other 
purposes,  it  is  necessary  to  carry  galvanized-iron  ducts  at  the  ceiling 
under  the  center  of  each  double  row  of  pews,  and  to  connect  \vith 
each  pair  by  means  of  branch  uptakes.  The  size  of  these  should 
be  equal  to  3  or  4  square  inches  for  each  occupant. 

Another  method  is  to  supply  the  air  through  a  small  register  in 
the  end  of  each  pew.  This  simplifies  the  pew  construction  some- 
what, but  otherwise  is  not  so  satisfactory  as  the  preceding  method. 


401 


206 


HEATING  AND  VENTILATION 


If  the  special  pew  construction  is  too  expensive,  or  for  any  othei 
reason  cannot  well  be  used,  and  the  fan  is  to  be  retained,  the  greater 
part  of  the  air  is  best  introduced  through  wall  registers  placed  about 
8  feet  above  the  floor,  with  exhaust  openings  at  or  near  the  floor. 
By  this  arrangement  the  air  is  thrown  horizontally  toward  the  center 
of  the  church,  and  much  of  it  falls  to  the  breathing  level  without 
rising  to  the  upper  part  of  the  room. 

Halls.  The  treatment  of  a  large  audience  hall  is  similar  to  that 
of  a  church,  the  warming  being  usually  done  in  one  of  the  three  ways 
already  described.  Where  a  fan  is  used,  the  air  is  commonly  delivered 

through  wall  registers  placed  in 
part  near  the  floor,  and  partly  at  a 
height  of  7  or  8  feet  above  it.  They 
should  be  made  of  ample  size, 
so  that  there  will  be  freedom  from 
draughts.  A  part  of  the  vents 
should  be  placed  in  the  ceiling, 
and  the  remainder  near  the  floor. 
All  ceiling  vents,  in  both  halls  and 
churches,  should  be  provided  with 
dampers  having  means  for  hold- 
ing them  in  any  desired  position. 
If  indirect  gravity  heaters  are 
used,  it  will  generally  be  necessary 
to  place  heating  coils  in  the  vent 
flues  for  use  in  mild  weather;  but 
if  the  fresh  air  is  supplied  by 
means  of  a  fan,  there  will  usually  be 

pressure  enough  in  the  room  to  force  the  air  out  without  the  aid  of 
other  means.  "When  the  vent  air-ways  are  restricted,  or  the  air  is 
impeded  in  any  way,  electric  ventilating  fans  are  often  used.  These 
give  especially  good  results  in  warmer  weather,  when  natural  venti- 
lation is  sluggish.  The  temperature  may  be  regulated  either  by 
using  the  double-duct  system  or  by  shutting  off  or  turning  on  a  greater 
or  less  number  of  sections  in  the  main  heater.  After  an  audience 
hall  is  once  warmed  and  filled  with  people,  very  little  heat  is  required 
to  keep  it  comfortable,  even  in  the  coldest  weather. 

Theaters.     In   designing   heating   and   ventilating   systems   for 


Fig.  174.    An  Approved  Method  of  De- 
livering Warm  Air  to  the  Audi- 
torium of  a  Church. 


402 


HEATING  AND  VENTILATION  207 

theaters,  a  wide  experience  and  the  greatest  care  are  necessary  to 
secure  the  best  results.  A  theater  consists  of  three  parts:  the  body 
of  the  house,  or  auditorium;  the  stage  and  dressing-rooms,  and  the 
foyer,  lobbies,  corridors,  stairways,  and  offices.  Theaters  are  usually 
located  in  cities,  and  surrounded  with  other  buildings  on  two  or  more 
sides,  thus  allowing  no  direct  connection  by  windows  with  the  ex- 
ternal air;  for  this  reason  artificial  means  are  necessary  for  providing 
suitable  ventilation,  and  a  forced  circulation  by  means  of  a  fan  is  the 
only  satisfactory  means  of  accomplishing  this.  It  is  usually  advisable 
to  create  a  slight  excess  of  pressure  in  the  auditorium,  in  order  that 
all  openings  shall  allow  for  the  discharge  rather  than  the  inward 
leakage  of  air. 

The  general  and  most  approved  method  of  air-distribution  is 
to  force  it  into  closed  spaces  beneath  the  auditorium  and  balcony 
floors,  and  allow  it  to  discharge  upward  through  small  openings 
among  the  seats.  One  of  the  best  methods  is  through  chair-legs 
of  special  latticed  design,  which  are  placed  over  suitable  openings  in 
the  floor;  in  this  way  the  air  is  delivered  to  the  room  in  small  streams, 
at  a  low  velocity,  without  draughts  or  currents.  The  discharge 
ventilation  should  be  largely  through  ceiling  vents,  and  this  may  be 
assisted  if  necessary  by  the  use  of  ventilating  fans.  Vent  openings 
should  also  be  provided  at  the  rear  of  the  balconies,  either  in  the  wall 
or  in  the  ceiling,  and  these  should  be  connected  with  an  exhaust  fan 
either  in  the  basement  or  in  the  attic,  as  is  most  convenient. 

The  close  seating  of  the  occupants  produces  a  large  amount  of 
animal  heat,  which  usually  increases  the  temperature  from  6  to  10 
degrees,  or  even  more;  so  that,  in  considering  a  theater  once  filled 
and  thoroughly  warmed,  it  becomes  more  of  a  question  of  cooling 
than  one  of  warming  to  produce  comfort. 

The  dressing-rooms  should  be  provided  with  a  generous  supply 
of  fresh  air,  sufficient  to  change  the  entire  contents  once  in  10  minutes 
at  least,  and  should  have  discharge  flues  of  sufficient  size  to  carry 
awa^r  this  amount  of  air  at  a  velocity  not  exceeding  300  feet  per 
minute,  unless  connected  with  an  exhaust  fan,  in  which  case  the 
velocity  may  be  doubled.  The  foyer,  corridors,  dressing-rooms, 
etc.,  are  generally  heated  by  direct  radiators,  which  may  be  con- 
cealed by  ornamental  screens  if  desired. 

Office  Buildings.     This  class  of  buildings  may  be  satisfactorily 


403 


20$  HEATING  AND  VENTILATION 


wanned  by  direct  steam,  hot  water,  or,  where  ventilation  is  desired, 
by  the  fan  system.  Probably  direct  steam  is  used  more  frequently 
than  any  other  system  for  this  purpose.  Vacuum  systems  are  well 
adapted  to  the  conditions  usually  found  in  this  type  of  building, 
as  most  modern  office  buildings  have  their  own  light  and  power 
plants,  and  the  exhaust  steam  can  thus  be  utilized  for  heating  pur- 
poses. The  piping  may  be  either  single  or  double.  If  the  former 
is  used,  it  is  better  to  carry  a  single  main  riser  to  the  upper  story,  and 
run  drops  to  the  basement,  as  by  this  means  the  steam  and  water 
flow  in  the  same  direction,  and  much  smaller  pipes  can  be  used  than 
would  be  the  case  if  risers  were  carried  from  the  basement  upward. 

Special  provision  must  be  made  for  the  expansion  of  the  risers  or 
drops  in  tall  buildings.  They  are  usually  anchored  at  the  center, 
and  allowed  to  expand  in  both  directions.  The  connections  with  the 
radiators  must  not  be  so  rigid  as  to  cause  undue  strains  or  to  lift  the 
radiators  from  the  floor. 

It  is  customary,  in  most  cases,  to  make  the  connections  with 
the  end  farthest  from  the  riser;  this  gives  a  length  of  horizontal  pipe 
which  has  a  certain  amount  of  spring,  and  will  care  for  any  vertical 
movement  of  the  riser  that  is  likely  to  occur.  Forced  hot-water 
circulation  is  often  used  in  connection  with  exhaust  steam.  The 
water  is  warmed  by  the  steam  in  large  heaters  similar  to  feed-water 
heaters  and  is  circulated  through  the  system  by  means  of  centrifugal 
pumps.  This  has  the  usual  advantage  of  hot  water  over  steam, 
inasmuch  as  the  temperature  of  the  radiators  may  be  regulated  to 
suit  the  conditions  of  outside  temperature. 

When  a  fan  system  is  used  the  arrangement  of  the  air-ways  is 
usually  somewhat  different  from  any  of  those  yet  described.  Owing 
to  the  great  height  of  these  buildings,  and  the  large  number  of  small 
rooms  which  they  contain,  it  is  impossible  to  carry  up  separate  flues 
from  the  basement.  One  of  the  best  arrangements  is  to  construct 
false  ceilings  in  the  corridor-ways  on  each  floor,  thus  forming  air- 
ducts  which  may  receive  their  supply  through  one  or  more  large  up- 
takes extending  from  the  basement  to  the  top  of  the  building.  These 
corridor  air-ways  may  be  tapped  over  the  door  of  each  room,  the 
openings  being  provided  with  suitable  regulating  dampers  for  gauging 
the  air-supply  to  each.  Adjustable  deflectors  should  be  placed  in 
the  main  air-shafts  for  proportioning  the  quantity  to  be  delivered 


404 


HEATING  AND  VENTILATION  209 

to  each  floor.  If  both  supply  and  discharge  ventilation  are  to  be 
provided,  the  fresh  air  may  be  carried  in  galvanized-iron  ducts  within 
the  ceiling  spaces,  and  the  remainder  used  for  conveying  the  exhausted 
air  to  uptakes  leading  to  a  discharge  fan  placed  upon  the  roof  of 
the  building.  In  both  of  these  cases,  it  is  assumed  that  heat  is  sup- 
plied to  the  rooms  by  direct  radiation,  and  that  the  air-supply  is  for 
ventilation  only. 

Apartment  Houses.  These  are  warmed  by  furnaces,  direct 
steam,  and  hot  water.  Furnaces  are  more  often  used  in  the  smaller 
houses,  as  they  are  cheaper  to  install,  and  require  a  less  skilful  at- 
tendant to  operate  them.  Steam  is  probably  used  more  than  any 
other  system  in  blocks  of  larger  size.  A  well-designed  single-pipe 
connection,  with  autcmatic  air-valves  dripped  to  the  basement,  is 
probably  the  most  satisfactory  in  this  class  of  work.  People  who 
are  more  or  less  unfamiliar  with  steam  systems  are  apt  to  overlook 
one  of  the  valves  in  shutting  off  or  turning  on  steam ;  and  where  only 
one  valve  is  used,  the  difficulty  arising  from  this  is  avoided.  Where 
pet-cock  air-valves  are  used,  they  are  often  left  open  through  careless- 
ness ;  and  the  automatic  valves,  unless  dripped,  are  likely  to  give  more 
or  less  trouble. 

Greenhouses  and  Conservatories.  Buildings  of  this  class  are 
heated  in  some  cases  by  steam  and  in  others  by  hot  water,  some  florists 
preferring  one  and  some  the  other.  Either  system,  when  properly 
designed  and  constructed,  should  give  satisfaction,  although  hot 
water  has  its  usual  advantage  of  a  variable  temperature.  The 
methods  of  piping  are,  in  a  general  wray,  like  those  already  described, 
and  the  pipes  may  be  located  to  run  underneath  the  beds  of  growing 
plants  or  above,  as  bottom  or  top  heat  is  desired.  The  main  is  gen- 
erally run  near  the  upper  part  of  the  greenhouse  and  to  the  farthest 
extremity,  in  one  or  more  branches,  with  a  pitch  upward  from  the 
heater  for  hot  water  and  with  a  pitch  downward  for  steam.  The 
principal  radiating  surface  is  made  of  parallel  lines  of  H  inch  or 
larger  pipe,  placed  under  the  benches  and  supplied  by  the  return 
current.  Figs.  175,  176,  and  177  show  a  common  method  of  running 
the  piping  in  greenhouse  work.  Fig.  175  shows  a  plan  and  eleva- 
tion of  the  building  with  its  lines  of  pipe;  and  Figs.  176  and  177  give 
details  of  the  pipe  connections  of  the  outer  and  inner  groups  of  pipes 
respectively. 


405 


210 


HEATING  AND  VENTILATION 


Any  system  of  piping  which  gives  free  circulation  and  which  is 
adapted  to  the  local  conditions,  should  give  satisfactory  results.  The 
radiating  surface  may  be  computed  from  the  rules  already  given. 
As  the  average  greenhouse  is  composed  almost  entirely  of  glass,  we 


Fig.  175.    Plan  and  Elevation  Showing  One  Method  of  Running  Piping  in  a  Greenhouse 

may  for  purposes  of  calculation  consider  it  such;  and  if  we  divide 
the  total  exposed  surface  by  4,  we  shall  get  practically  the  same 
result  as  if  we  assumed  a  heat  loss  of  85  B.  T.  U.  per  square  foot  of 
surface  per  hour,  and  an  efficiency  of  330  B.  T.  U.  for  the  heating 


408 


HEATING  AND  VENTILATION  211 

coils;  so  that  we  may  say,  in  general,  that  the  square  feet  of  radiating 
surface  required  equals  the  total  exposed  surface,  divided  by  4  for 
steam  coils,  and  by  2.5  for  hot-water.  These  results  should  be  in- 
creased from  10  to  20  per  cent  for  exposed  locations. 

CARE  AND  MANAGEMENT 

The  care  of  furnaces,  hot-water  heaters,  and  steam  boilers  has 
been  discussed  in  connection  with  the  design  of  these  different  systems 
of  heating,  and  need  not  be  repeated.  The  management  of  the 
heating  and  ventilating  systems  in  large  school  buildings  is  a  matter 
of  much  importance,  especially  in  those  using  a  fan  system.  To  obtain 
the  best  results,  as  much  depends  upon  the  skill  of  the  operating 
engineer  as  upon  that  of  the  designer. 

Beginning  in  the  boiler-room,  he  should  exercise  special  care 
in  the  management  of  his  fires,  and  the  instruction  given  in  "Boiler 
Accessories"  should  be  carefully  followed;  all  flues  and  smoke 
passages  should  be  kept  clear  and  free  from  accumulations  of  soot 
and  ashes  by  means  of  a  brush  or  steam  jet.  Pumps  and  engine  should 
be  kept  clean  and  in  perfect  adjustment,  and  extra  care  should  be 
taken  when  they  are  in  rooms  through  which  the  air-supply  is  drawn,, 
or  the  odor  of  oil  will  be  carried  to  the  rooms.  All  steam  traps  should 
be  examined  at  regular  intervals  to  se'e  that  they  are  in  working  order; 
and  upon  any  sign  of  trouble,  they  should  be  taken  apart  and  care- 
fully cleaned. 

The  air-valves  on  all  direct  and  indirect  radiators  should  be 
inspected  often;  and  upon  the  failure  of  any  room  to  heat  properly, 
the  air-valve  should  first  be  looked  to  as  a  probable  cause  of  the  diffi- 
culty. Adjusting  dampers  should  be  placed  in  the  base  of  each  flue, 
so  that  the  flow  to  each  room  may  be  regulated  independently.  In 
starting  up  a  new  plant,  the  system  should  be  put  in  proper  balance 
by  a  suitable  adjustment  of  these  dampers;  and,  when  once  adjusted, 
they  should  be  marked,  and  left  in  these  positions.  The  temperature 
of  the  rooms  should  never  be  regulated  by  closing  the  inlet  registers. 
These  should  never  be  touched  unless  the  room  is  to  be  unused  for 
a  day  or  more. 

In  designing  a  fan  system,  provision  should  be  made  for  air- 
rotation;  that  is,  the  arrangement  should  be  such  that  the  same 
air  may  be  taken  from  the  building  and  passed  through  the  fan  and 


407 


212  HEATING  AND  VENTILATION 


Fig.  176.    Connections  of  Outer  Groups  of  Pipes  of  Greenhouse  Shown  in  Fig.  175. 


Fig.  177.    Connections  of  Inner  Groups  of  Pipes  of  Greenhouse  Shown  in  Fig.  175. 


408 


HEATING  AND  VENTILATION  213 

heater  continuously.  This  is  usually  accomplished  by  closing  the 
main  vent  flues  and  the  cold-air  inlet  to  the  building,  then  opening  the 
class-room  doors  into  the  corridor-ways,  and  drawing  the  air  down 
the  stair-wells  to  the  basement  and  into  the  space  back  of  the  main 
heater  through  doors  provided  for  this  purpose.  In  warming  up  a 
building  in  the  morning,  this  should  always  be  done  until  about 
fifteen  minutes  before  school  opens.  The  vent  flues  should  then  be 
opened,  doors  into  corridors  closed,  cold-air  inlets  opened  wide,  and 
the  full  volume  of  fresh  air  taken  from  out  of  doors. 

At  night  time  the  dampers  in  the  main  vents  should  be  closed, 
to  prevent  the  warm  air  contained  in  the  building  from  escaping. 
The  fresh  air  should  be  delivered  to  the  rooms  at  a  temperature  of 
from  70  to  75  degrees;  and  this  temperature  must  be  obtained  by 
proper  use  of  the  shut-off  valves,  thus  running  a  greater  or  less  number 
of  sections  on  the  main  heater.  A  little  experience  will  show  the 
engineer  how  many  sections  to  carry  for  different  degrees  of  outside 
temperature.  A  dial  thermometer  should  be  placed  in  the  main 
warm-air  duct  near  the  fan,  so  that  the  temperature  of  the  air  delivered 
to  the  rooms  can  be  easily  noted. 

The  exhaust  steam  from  the  engine  and  pumps  should  be  turned 
into  the  main  heater;  this  will  supply  a  greater  number  of  sections 
in  mild  weather  than  in  cold,  owing  to  the  less  rapid  con- 
densation. 


409 


PLUMBING. 

PART     I. 


PLUMBING  FIXTURES. 

Bath  Tubs.  There  are  many  varieties  of  bath  tubs  in  use  at 
the  present  time,  ranging  from  the  wooden  box  lined  with  zinc  or 
copper  which  was  in  common  use  a  number  of  years  ago  and  is 
still  to  be  found  in  the  old  houses,  to  the  finest  crockery  and 
enameled  tubs  which  are  now  used  in  the  best  modern  plumbing. 
In  selecting  a  tub  we  should  choose  one  with  as  little  woodwork 
about  it  as  possible.  Those  lined  with  zinc  or  copper  are  hard  to 
keep  clean  and  are  liable  to  leak  and  are,  therefore,  undesirable 
from  a  sanitary  standpoint.  The  plain  cast  iron  tub,  painted,  is 
the  next  in  cost.  This  makes  a  serviceable  and  satisfactory  tub  if 


Fig.  1. 

kept  painted ;  it  is  used  quite  extensively  in  asylums,  hospitals, 
etc.  One  of  this  type  is  shown  in  Fig.  1.  These  are  sometimes 
galvanized  instead  of  being  painted. 

The  "steel-clad"  tub  shown  in  Fig.  2  is  a  good  form  for  a 
low-priced  article.  This  tub  is  formed  of  sheet  steel  and  has  a 
lining  of  copper.  This  form  is  light  and  easy  to  handle ;  it  is  an 
open  fixture  the  same  as  the  cast  iron  tub  and  requires  no  casing. 
It  is  provided  with  cast  iron  legs  and  a  wooden  cap.  Probably 
the  most  common  form  to  be  found  in  the  average  house  at  the 
present  time  is  the  porcelain  lined  iron  tub  as  shown  in  Fig.  3. 


411 


I 


PLUMBING. 


This  has  a  smooth  interior  finish  and  is  easily  kept  clean.  It  will 
not,  however,  stand  the  hard  usage  of  those  above  described  as 
the  lining  is  likely  to  crack  if  struck  by  any  hard  substance. 

In  Fig.  4  is  shown  a  crockery  or  porcelain  tub  arranged  for 
needle  and  shower  baths.  This  is  a  most  sanitary  article  in  every 
respect  and  requires  no  woodwork  of  any  kind;  being  made  of  one 


Fig.  2. 


piece,  there  is  no  chance  for  dirt  to  collect,  it  is  a  heavy  tub  anci 
requires  great  care  in  handling.  This  material  is  very  cold  to  the 
touch  until  it  has  become  thoroughly  warmed  by  the  hot  water. 
Fig.  5  shows  a  seat  bath  and  Fig.  6  a  foot  bath,  both  of  which  are 


Fig.  3. 

very  convenient  and  should  be  placed  in  all  well  equipped  bath 
rooms  if  the  expense  does  not  prohibit  their  use. 

Water  Closets.  There  is  a  great  variety  of  water  closets 
from  which  to  choose,  many  operating  upon  the  same  principle 
but  varying  slightly  in  form  and  finish.  The  best  are  made  of 


412 


PLUMBING. 


porcelain,  the  bowl  and  trap  being  in  one  piece  without  corners  or 
crevices  so  that  they  are  easily  kept  clean,  The  top  of  the  bowl 
is  provided  with  a  wooden  rim  and  cover.  The  general  arrange- 
ment of  seat  and  flushing  tank  is  shown  in  Fig.  7.  A  section 
through  the  bowl  is  shown  in  Fig.  8.  This  type  is  known  as  a 


Fig.    4. 

syphon  closet,  and  those  made  on  this  principle  are  probably  the 
most  satisfactory  of-any  in  present  use.  They  are  made  in  differ- 
ent forms  by  various  manufacturers  but  each  involves  the  prin- 
ciple which  gives  it  its  name.  Water  stands  in  the  bottom  as 
ihown,  thus  forming  a  seal  against  gases  from  the  sewer. 


413 


6 


PLUMBING. 


When  the  closet  is  flushed,  water  rushes  down  the  pipe  and  fills 
the  small  chamber  at  the  rear  which  discharges  in  a'  jet  at  the 
bottom  as  shown  by  the  arrow.  The  syphon  action  thus  set  up 
draws  the  entire  contents  of  the  bowl  over  into  the  soil  pipe.  In 
the  meantime  a  part  of  the  water  from  the  tank  fills  the  hollow 
rim  of  the  bowl  and  is  discharged  in  a  thin  stream  around  the 


Fig.  5. 


Fig.  7. 


entire  perimeter  which  thoroughly  washes  the  inside  of  the  bowl 
each  time  it  is  flushed.  Fig.  9  shows  a  form  called  the  "wash- 
out" closet.  In  this  case  the  whole  of  the  water  is  discharged 
through  the  flushing  rim  but  with  greater  force  at  the  rear  which 
washes  the  contents  of  the  upper  bowl  into  the  lower  which  over- 
flows into  the  soil  pipe.  This  is  a  good  form  of  closet  and  is 
widely  used.  A  similar  form,  but  without  the  upper  bowl  is 


414 


PLUMBING. 


shown  in  Fig.  10.  This  is  known  as  the  "wash  down"  closet 
and  operates  in  the  manner  already  described.  The  water  enters 
the  bowl  through  the  flushing  rim  and  discharges  its  contents  by 


Fig.  8. 


Fig.  9. 


overflowing  into  the  soil  pipe.     This  is  a  simple  form  of  closet 
and  easily  kept  clean. 

One  of  the  simplest  closets  is  the  "hopper"  shown  in  Fig.  11. 
This  consists  of  a  plain  bowl  of  porcelain  or  cast  iron  tapering  to 


Fig.  10. 


Fig.  11. 


an  outlet  about  4"  in  diameter  at  the  bottom.  It  is  connected 
directly  with  the  soil  pipe  as  shown.  The  trap  may  be  placed 
either  above  the  floor  or  below  as  desired.  They  are  provided 
with  a  flushing  rim  at  the  top  similar  to  that  already  described. 
This  type  of  closet  is  the  cheapest  but  at  the  same  time  the  least 
satisfactory  of  any  of  the  different  kinds  shown. 


415 


PLUMBING. 


It  is  sometimes  desirable  to  place  a  closet  in  a  location  where 
there  would  be  danger  of  freezing  if  the  usual  form  of  flushing 
tank  was  used.  Fig.  12  shows  an  arrangement  which  may  bs 
used  in  a  case  of  this  kind.  The  valve  and  water  connections  are 
placed  below  the  frost  line  and  a  pipe  not  shown  in  the  cut  is 
carried  up  to  the  rim  of  the  bowl.  Whenthe  rim  is  shutdown  the 


Fig.  12. 

valve  is  opened  by  means  of  the  chain  attached  to  it  and  water 
flows  through  the  bowl  while  in  use.  When  released,  the  weight 
on  the  lever  closes  the  valve  and  raises  the  wooden  rim  to  its 
original  position.  Any  water  which  remains  in  the  flush  pipe  is 
drained  to  the  soil  pipe  through  a  small  drip  pipe  which  is  seen  in 
the  cut. 

Urinals.  A  common  form  of  urinal  is  shown  in  Fig.  13. 
The  partitions  and  slab  at  the  back  are  either  of  slate  or  marble 
and  the  bowl  of  porcelain.  They  may  be  flushed  like  a  closet. 
Fig.  14  shows  a  section  through  the  bowl  and  indicates  the 


416 


PLUMBING. 


manner  of  flushing,  partly  through  the  rim  and  partly  at  the  back. 
The  trap  or  seal  is  shown  at  the  bottom.  Another  form  is  shown 
in  Fig.  15.  In.  this  case  the  bowl  remains  partly  filled  with 
water  which  forms  a  seal  as  shown.  It  is  flushed  both  through 
the  rim  and  the  passage  at  the  back.  In  action  it  is  the  same  as 
the  syphon  closet  shown  in  Fig.  8  and  the  bowl  is  drained  each 


Fig.  13. 


Fig.  14. 


time  it  is  flushed,  but  immediately  fills  with  water  to  the  level 
indicated. 

An  automatic  flushing  device  is  illustrated  in  Fig.  16.  When 
the  water  line  in  the  tank  reaches  a  given  level,  the  float  lever 
releases  a  catch  and  flushes  the  urinal.  The  intervals  of  flushing 
can  be  regulated  by  adjusting  the  cock  shown  in  the  inlet  pipe, 
near  the  bottom  of  the  tank. 

A  simple  form  of  urinal  commonly  used  in  schools  and  public 
buildings  is  shown  in  Fig.  17.  This  is  flushed  by  means  of 


417 


10 


PLUMBING. 


small  streams  of  water  which  are  dis- 
charged through  the  perforated  pipe 
near  the  top  of  the  slab  at  the  back 
and  run  down  in  a  thin  sheet  to  the 
gutter  at  the  bottom. 

Lavatories.  Bowls  and  lava- 
tories can  be  had  in  almost  any  form. 
Fig.  18  shows  a  simple  corner  lava- 
tory, made  of  porcelain  and  provided 


Fig.  17. 


16. 

with  hot  a  n  d 
cold  water  fau- 
cets. It  has  an 
overflow,  shown 
by  the  s  in  a  1 1 
openings  at  the 
back  and  a  rub- 
ber plug  for  clos- 
ing the  drain  at 
the  bottom. 

The  lavatory 
shown    in    Fig. 

19  is    provided 
wi  t  h   in  a  rb  ie 
slabs  and  is  more 
expensive.    Fig. 

20  shows  a  sec- 
tion through  the 
b  o  w  1 .         T  h  e 
waste  pipe  is  at 
the  back,  which 


418 


PLUMBING. 


11 


brings  the  plug  and  chain  well  out  of  the  way.  A  pattern  still 
more  elaborate  is  shown  in  Fig.  21,  and  a  section  through  the 
bowl  in  Fig.  22.  The  waste  pipe  plug  in  this  case  is  in  the 
form  of  a  hollow  tube  and  acts  as  an  overflow  when  closed  and 
as  a  strainer  when  open.  It  is  held  open  by  means  of  a  slot  and 


Fig.  18. 


Fig.  19. 


pin  near  the  top.  Fig.  23  shows  a  bowl  so  arranged  that  either 
hot,  cold  or  tepid  water  may  be  drawn  through  the  same  opening 
which  is  placed  well  down  in  the  bowl  where  it  is  out  of  the  way. 


Fig.  20. 

Sinks.  Sinks  are  made  of  plain  wood,  and  of  wood  lined 
with  sheet  metal,  such  as  copper,  zinc  or  galvanized  iron.  They 
are  also  made  of  sheet  steel,  cast  iron,  either  plain,  galvanized  or 
enameled,  and  of  soapstone  and  porcelain.  Each  has  its  advan- 
tages and  disadvantages.  The  wooden  sink  is  liable  to  leak, 


419 


12 


PLUMBING. 


and  is  difficult  to 
keep  thoroughly 
clean.  The  lined 
sink  is  most  satis- 
factory when  new, 
but  holes  are  quite 
easily  cut  or 
punched  through 
the  lining  and  it 
then  becomes  very 
objectionable  from 
a  sanitary  stand- 
point as  the  greasy 
water  and  vege- 
table matter  which 
works  through  the 
opening  causes  the 
woodwork  to  decay 
rapidly  and  to  give 
off  in  the  process 
a  gas  which  is  not 
only  unhealthful  but 
the  underside  so  that 


Fig.  21. 

tends  to  destroy  the  lining  of  the  sink  from 
its  destruction  is  rapid  after  a  leak  is  once 
started.  The  cast 
iron  sink  is  satisfac- 
tory. The  appearance 
is  improved  by  galvan- 
izing, but  this  soon 
wears  off  on  the  in- 
side.  Enameled 
sinks  are  easily  kept 
clean  but  likely  to 
become  cracked  or 
broken  from  hard 
usage  or  from  ex- 
tremes of  hot  or  cold ; 

22  the  porcelain  sink  has 

the  same   defects; 


420 


PLUMBING. 


18 


they  are  both  however  well  adapted  to  places   where  they  will 
receive  careful  usage. 

Taking  all  points  into  consideration  the  soapstone  sink  may 
perl  laps   be  considered  the  most   satisfactory  for  all-around  use. 


Jt  will  not  absorb  moisture  ;  is  not  affected  by  the  action  of  acids, 
oil  (.r  grease  will  not  enter  the  pores  and  it  is  not  injured  by  hot 
water  nor  liable  to  crack. 

Fig.  24  shows  the  ordinary  cast  iron  sink,  made  to  be  set  in 
a  wooden  casing  ;  this  is  not  to  be  recommended  however,  and  it  is 


Fig.  24. 

much  better  to  support  them  upon  iron  brackets  or  legs.  Fig.  25 
shows  an  enameled  sink  mounted  in  this  way.  A  porcelain  sink 
with  dish  racks  is  shown  in  Fig.  26.  This  is  a  good  form  for  a 
pantry  sink  which  is  used  only  for  washing  cutlery,  glassware, 


421 


14 


PLUMBING. 


crockery,  etc.,  and  is  not  subjected  to  hard  usage.  A  slop  sink  is 
shown  in  Fig.  27.  This,  as  will  be  noticed,  is  provided  with  an 
extra  large  waste  pipe  and  trap  to  prevent  clogging.  These  sinks 
are  made  of  cast  iron  with  different  finishes  and  of  porcelain. 

Set  tubs  for  laundry  use  are  made  of  soapstone,  slate,  cast 


Fig.  25. 

iron  (enameled  or  galvanized)  and  of  porcelain.  What  has  been 
said  in  regard  to  kitchen  sinks  applies  equally  well  in  this  case. 

A  set  of  enameled  tubs  is  shown  in  Fig.  28. 

Traps.  A  trap  is  a  loop  or  water  seal  placed  in  a  pipe  to  pre- 
vent the  gases  from  the  drain  or  sewer  from  passing  up  through  the 
waste  pipes  of  the  fixtures  into  the  rooms.  A  common  form  made 
up  of  cast  iron  pipe  and  known  as  a  "running  trap"  is  shown  in 
Fig.  29.  A  trap  of  this  form  is  placed  in  the  main  drain  pipe  of  a 


422 


PLUMBING. 


building  outside  of  all  the  connections  to  prevent  gases  from  the 
main  sewer  or  cesspool  from  entering  the  building.  A  removable 
cover  is  placed  on  top  of  the  trap  -to  give  access  for  cleaning. 

The  floor  trap  shown  in  section  in  Fig.  30  is  made  both  of 
brass  and  of  lead.  It  is  commonly  used  for  kitchen  sinks  and  is 
placed  on  the  floor  just  beneath  the  fixture.  It  is  provided 
with  a  removable  trap  screw  or  clean-out  for  use  when  it  is  desired 


Fig.  26. 

to  remove  grease  or  sediment  from  the  interior.  Fig.  31  shows  a 
common  form  for  lavatories,  which  consists  simply  of  a  loop  in  the 
waste  pipe.  These  are  usually  made  of  brass  and  nickle  plated 
when  used  with  open  fixtures.  A  trap  for  similar  purposes  is 
shown  in  Figs.  32  and  33. 

Figs.  34  and  35  show  a  form  known  as  the  centrifugal  trap  on 
account  of  the  rotary  or  whirling  motion  given  to  the  water  by 
the  peculiar  arrangement  of  the  inlet  and  outlet.  This  motion 
carries  all  solid  particles  to  the  outside  and  discharges  them  with 
the  water,  thus  keeping  the  trap  clear  of  sediment.  Where  there 
is  likely  to  be  a  large  amount  of  grease  in  the  water  as  in  the  case 
of  waste  from  a  hotel  or  restaurant  it  becomes  necessary  to  use  a 
special  form  of  separating  trap  to  prevent  the  waste  pipes  from  becom- 


423 


PLUMBING. 


big  clogged.  A  grease  trap  designed  for  this  purpose  is  shown  in 
Fig,  36.  .Its  action  is  readily  seen  as  the  fatty  matter  will  be 
separated,  first  by  dropping  into  a  large  body  of  cold  water  and 
then  being  driven  against  the  center  partition  before  an  outlet  can 
be  gained.  The  grease  then  rises  to  the  surface  where  it  cools 
and  can  then  be  easily  removed  as  often  as  necessary. 

Sometimes  a  cellar  or  basement  is  drained  into  a  sewer  which 


Tig.  27. 

is  liable  to  be  filled  at  high  tide  or  from  other  causes  and  a 
special  trap  or  check  must  be  used  to  pi-event  the  cellar  from 
becoming  flooded.  Such  a  trap  i*  shown  in  Fig.  37.  When 
water  flows  in  from  below,  the  float  rises,  and  the  rubber  rim 
pressing  against  the  valve  seat  prevents  any  passage  through  the 
trap;  the  cut  shows  the  valve  closed  by  the  action  of  high  water. 
Tanks  or  cisterns  for  flushing  closets  or  other  fixtures  are 
usually  made  of  wood  and  lined  with  zinc  or  copper.  These  are 
generally  placed  inside  a  finished  casing.  A  common  form  is  shown 


424 


PLUMBING. 


17 


in  Fig.  38.  The  arrangement  of  valves  for  supplying  water  to 
the  tank  and  for  flushing  the  fixtures  is  shown  in  Fig.  39.  The 
large  float  or  ball  cock  regulates  the  flow  of  water  into  the  tank 
from  the  street  main  or  house  tank.  When  the  water  in  the  tank 


Fig.  28. 


falls  below  a  certain  level  the  float  drops  and  opens  a  valve,  thus 
admitting  more  water,  and  closes  again  when  the  tank  is  filled. 
The  closet  is  flushed  by  pulling  a  chain  attached  to  the  lever  at 
the  right  which  opens  the  valve  in  the  bottom  of  the  tank  and 
admits  water  to  the  flushing  pipe.  In  this  form  the  valve  remains 
open  only  while  the  lever  is  held  down  by  the 
chain,  the  weight  on  the  other  end  of  the  lever 
closing  the  valve  as  soon  as  the  chain  is  released. 
Another  form  which  is  partially  automatic  is 
shown  in  Fig.  40.  When  the  chain  is  pulled 
it  raises  the  central  valve  from  its  seat  and 
allows  the  water  to  flow  down  the  flush  pipe 
until  the  tank  is  nearly  empty.  When  empty,  the  strong  suction 
seals  the  valve  which  remains  closed  until  the  ehain  is  again 
pulled.  In  this  type  of  valve  a  single  pull  of  the  chain  is  suffi- 
cient to  flush  the  closet  without  further  attention. 

A  purely  automatic    flushing   device   is  shown  in  Fig.   41. 


Fig.  29. 


18 


PLUMBING. 


The  chain  in  this  case  is  attached  to  the  rim  of  the  seat  so  that 
when  it  is  pressed  down,  the  valve  in  the  compartment  at  the 
bottom, connecting  with  the  flush  pipe  is  closed  awd  at  the  same  time 


Fig.  33. 


communication  is  opened  between  the  two  compartments.  When 
the  pull  on  the  chain  is  released  the  valve  connecting  the  flush 
pipe  is  opened  and  the  opening  between  the  compartments  closed 


PLUMBING. 


19 


Fig.  34. 


Fig.  35. 


427 


20 


PLUMBING. 


so  that  the  water  in  the  lower  portion  of  the  tank  flows 
through  the  flush  pipe  into  the  closet  automatically,  and.  \vhen 
empty  no  more  can  be  admitted  until  the  lever  is  again  polled 
down  and  the  valve  in  the  partition  opened. 


Fig.  37. 

Faucets.  There  are  many  different  forms  of  faucets  in 
use.  The  most  common  is  the  c6mpression  cock  shown  in  Fig. 
42.  This  has  a  removable  leather  or  asbestos  seat  which 
requires  renewing  from  time  to  time  as  it  becomes  worn. 
Fig.  43  shows  a  similar  form,  in  which  the  valve  seat  is 
free  to  adjust  itself,  being  held  in  place  by  a  spring.  Another 


Fig.  38. 


Fig.  39. 


style  often  vised  in  hotels  and  other  public  places  is  the  self-closing 
faucet.  These  are  fitted  with  springs  in  such  a  way  that  they 
remain  closed  except  when  held  open.  Two  different  forms  are 
shown  in  Figs.  44  and  45. 

There  are  various  arrangements  for  mixing  the  hot  and  cold 
water  for  bowls  and  bath  tubs  before  it  is  discharged.     This  is 


423 


PLUMBING. 


21 


accomplished  by  having  both  faucets  connect  with  a  common  nozzle. 
Such  a  device  for  a  lavatory  is  shown  in  Fig.  46. 


Fig.  40. 


Fig.  41. 


Fig.  42. 


Fig.  48. 


SOIL  AND  WASTE  PIPES. 

Cast=Iron  Pipe.  There  are  many  different  forms  of  soil  pipes 
and  fittings,  and  one  can  best  acquaint  himself  with  these  by 
looking  over  the  catalogues  of  different  manufacturers.  Figs.  47 
and  48  show  two  lengths  of  soil  pipe ;  the  first  is  the  regular 
pattern,  having  only  one  hub,  and  the  second  is  a  length  of  double- 
hub  pipe  ;  this  can  be  used  to  good  advantage  where  many  short 
pieces  are  required. 

Figs.  49  to  57  show  some  of  the  principal  soil  pipe  fittings. 
Figs.  49,  50,  51,  52  and  53  show  quarter,  sixth,  eighth,  sixteenth 


429 


PLUMBING. 


and  return  bends  respectively,  and  by  the  use  of  these  almost  any 
desired  angle  can  be  obtained.  Different  lines  of  pipe  may  be 
connected  by  means  of  the  Y  and  T-Y  branches  shown  in  Figs. 


Fig.  44. 


Fig.  46. 


54,  55,  56  and  57.  The  T-Y  fitting,  Fig.  56,  is  used  in  place  of 
the  Y  branch,  Fig.  54,  in  cases  where  it  is  desired  to  connect  two 
pipes  which  run  perpendicular  to  each  other. 

The  double  T-Y,  Fig.  57,  is  conven- 
ient for  use  in  double  houses  where  a  single 
soil  pipe  answers  for  two  lines  of  closets. 
Pipe  Joints,  Great  care  should  be 
given  to  making  up  the  joints  in  a  proper 
manner,  as  serious  results  may  follow  any 
defective  workmanship  which  allows  sewer 
gas  to  escape  into  the  building.  In  mak- 
ing up  a  joint,  first  place  the  ends  of  the 
pipes  in  position  and  fasten  them  rigidly, 
then  pack  the  joint  with  the  best  picked 
oakum.  In  packing  the  oakum  around 
the  hub,  the  first  layer  must  be  twisted  into  a  small  rope  so  that 
it  will  drive  in  with  ease  and  still  not  pass  through  to  the  inside 
of  the  pipe  where  the  ends  join. 


Fig. 


430 


PLUMBING. 


In  a  4-inch  pipe  the  packing  should  be  about  1  inch  in  thick- 
ness and  calked  perfectly  tight  so  that  it  will  hold  water  of  itself 
without  the  lead.  Just  before  the  packing  is  driven  tightly  into 


Fig.  47. 


Fig.  48. 


Fig.  49. 


Fig.  50. 


Fig.  51. 


Fig.  52. 


Fig.  53. 


Fig.  54. 


the  hub,  the  joint  should  be  examined  to  see  that  the  space  around 
the  hub  is  the  same,  so  that  the  lead  will  flow  evenly  and  be  of 
the  same  thickness  at  all  points,  as  the  expansion  and  contraction 


431 


24 


PLUMBING. 


will  work  an  imperfect  joint  loose  much  sooner  than  one  in  which 
the  lead  is  of  an  even  thickness  all  the  way  around.  Only  the 
best  of  clean  soft  lead  should  he  used  for  this  purpose.  In  calking 
in  the  lead  after  it  has  been  poured,  great  care  must  be  exercised, 
as  the  pipe,  if  of  standard  grade,  is  easily  cracked  and  will  stand 
but  little  shock  from  the  calking  chisel  and  hammer. 

Fig.  58  shows  a  section  through  the  calked  joint  of  a  cast 
iron  soil  pipe. 


Fig.  56. 


Fig.  57. 


Wrought  Iron  Pipe.  This  is  used  but  little  in  connection 
with  the  waste  pipes  except  for  the  purpose  of  back  venting  where 
it  may  be  employed  with  screwed  joints  the  same  as  in  steam 
work.  It  is  sometimes  used  where  only  small  drain  pipes  are 


Fig.  58. 

necessary,  but  is  not  desirable  as  it   is  likely  to  become  choked 
with  rust  or  to  be  eaten  through  by  moisture  from  the  outside. 

Brass  Pipe.  Brass  pipe,  nickle  plated,  is  largely  used  for 
connecting  open  fixtures,  such  as  lavatories  or  bath  tubs,  with  the 
soil  pipe.  It  is  common  to  use  this  for  the  exposed  portions  of 
the  connections  and  to  use  lead  for  that  part  beneath  the  floor  or 
in  partitions.  The  various  fittings  are  also  made  of  brass  and 
finished  in  a  similar  manner. 


432 


PLUMBING. 


25 


Lead  Pipe.  For  sinks,  bath  tubs,  ]aundry  tubs,  etc.,  noth- 
ing is  better  for  carrying  off  the  waste  water  than  lead  pipe,  for 
the  reason  that  it  has  a  smooth  interior  surface  which  offers  a 
small  resistance  to  the  flow  of  water,  and  does  not  easily  collect 
dirt  or  sediment.  It  can  also  be  bent  in  easy  curves  which  is  an 
advantage  over  fittings  which  make  abrupt  turns ;  this  is  especi- 
ally important  in  pipes  of  small  size. 

Pipe  Joints.  There  are  two.  common  methods  of  making 
joints  in  lead  pipe,  known  as  the  "  cup  joint "  and  the  "  wipe 
joint."  The  first  is  suitable  only  on  small  pipes  or  very  light 
pressures.  This  is  made  by  flanging  the  end  of  one  of  the  pipes 
and  inserting  the  other,  then  filling  in  the  flange  with  solder  by 
means  of  a  soldering  iron,  see  Fig.  59.  In  making  this  joint  great 


SOLDER 


Fig.  59. 


Fig.  60. 


care  should  be  taken  that  the  ends  of  the  pipes  are  round  and  fit 
closely  so  there  will  be  no  chance  for  the  solder  to  run  through 
inside  the  pipe  and  form  obstructions  for  the  collection  of 
sediment. 

The  different  stages  of  a  wipe  joint  are  shown  in  Fig.  60. 
The  ends  of  the  pipes  are  first  cleaned  and  then  fitted  together 
as  shown  in  the  second  stage.  The  solder  is  melted  in  a  small 
cast  iron  crucible  and  is  carefully  poured  on  the  joint  or  thrown 
on  with  a  small  stick  called  a  "spatting  stick."  As  the  solder 
cools  it  becomes  pasty  and  the  joint  can  be  worked  into  shape  by 
means  of  the  stick  or  a  soft  cloth,  or  both,  depending  upon  the 
kind  of  joint  and  stage  of  operation.  The  filial  shape  and  smooth 
finish  is  given  with  the  cloth.  The  ability  to  make  a  joint  of  this 
kind  can  be  attained  only  by  practice,  and  printed  directions  are 


433 


26 


PLUMBING. 


of  little  value  as  compared  with  observation  and  actual  practice. 
This  is  the  strongest  and  most  satisfactory  joint  that  can  be  made 
between  two  lead  pipes  or  a  lead  and  brass  or  copper  pipe.  In 
the  latter  case  the  brass  or  copper  should  be  carefully  tinned  as 
far  as  the  joint  is  to  extend  by  means  of  a  soldering  iron. 

Where  lead  waste  pipes  are  to  be  connected  with  cast  iron 
soil  pipts  a  brass  ferule  should  be  used.  Different  forms  of  these 
are  shown  in  Figs.  Gl  and  02.  The  lead  pipe  is  wiped  to  the 
finished  end  of  the  ferule  while  the  other  end  is  calked  into  the 
hub  of  the  cast  iron  pipe  in  the  manner  already  described.  The 
ferule  should  be  made  heavy  so  as  not  to  be  injured  in  the  proc- 


F/N/S/-/ED 


HUB 


Fig.  61. 


ess    of   calking.       Cup    joints    should     never    be    used    for    this 
purpose. 

Tile  Pipes.  Nothing  but  metal  piping  should  be  used  inside 
of  a  building,  but  in  solid  earth,  starting  from  a  point  about  10 
feet  away  from  the  cellar  wall,  we  may  use  salt-glazed,  vitrified,  or 
terra  cotta  pipe  for  making  the  connection  with  the  main  sewer. 
This  pipe  is  made  in  convenient  lengths  and  shapes  and  is  easily 
handled.  Various  fittings  are  made  similar  in  form  to  those 
already  described  for  cast  iron.  In  laying  tile  pipe  each  piece 
should  be  carefully  examined  to  see  that  it  is  smooth,  round,  and 
free  from  cracks.  The  ends  should  fit  closely  all  around,  and  each 
length  of  pipe  should  fit  into  the  next  the  full  length  of  the  hub. 
In  making  the  joints  nothing  but  the  best  hydraulic  cement  should 
be  used,  and  great  care  should  be  taken  that  this  is  pressed  well 


434 


PLUMBING.  27 


into  the  space  between  the  two  pipes.  All  cement  that  works 
.through  into  the  interior  should  be  carefully  removed  by  means  of 
a  swab  or  brush  made  especially  for  this  purpose.  The  earth 
should  be  filled  in  around  a  pipe  of  this  kind  before  the  cement  is 
set  or  else  the  joints  are  likely  to  crack.  Fine  soil  should  be  filled 
in  around  the  pipe  to  a  depth  of  3  or  4  inches,  and  rammed  down 
solid,  and  the  ditch  may  then  be  filled  in  without  regard  to  the 
pipe.  No  tile  pipe  should  be  used  inside  of  a  house  or  nearer 
than  about  10  feet  for  the  reason  it  might  not  stand  the  pressure 
in  case  a  stoppage  should  occur  in  the  sewer.  This  kind  of  pipe 
is  not  intended  to  carry  a  pressure  and  when  used  in  this  way 
is  seldom  entirely  filled  with  water.  Joints  between  iron  and  tile 
piping  are  made  with  cement  in  the  manner  described  for  two 
sections  of  tile. 

Cesspools.  It  is  often  desired  to  install  a  system  '»f  plumb- 
ing in  a  building  in  the  country  or  in  a  village  where  there  is  no 
system  of  sewerage  with  which  to  connect.  In  this  case  it  becomes 
necessary  to  construct  a  cesspool.  This  is  always  undesirable,  but 
if  properly  constructed  and  placed  at  a  suitable  distance  from  the 
house  and  in  such  a  position  that  it  cannot  drain  into  a  well  or 
other  source  of  water  supply  it  may  be  used  with  comparative 
safety.  Especial  care  should  be  taken  in  the  construction,  and 
when  in  use  it  should  be.  regularly  cleaned.  One  form  of  cess- 
pool is  shown  in  Fig.  63.  This  consists  of  two  brick  chambers 
located  at  some  distance  from  the  building  and  in  a  position  where 
the  ground  slopes  away  from  it  if  possible.  The  larger  chamber 
has  a  clean-out  opening  in  the  top  which  should  be  provided  with 
an  air-tight  cover.  An  ordinary  cast  iron  cover  may  be  made 
sufficiently  tight  by  covering  it  over  with  3  or  4  inches  of  earth 
packed  solidly  in  place.  A  vent  pipe  should  be  carried  from  the 
top  to  such  a  height  that  all  gases  will  be  discharged  at  an  eleva- 
tion sufficient  to  prevent  any  harm. 

The  smaller  chamber  is  connected  with  the  first  by  means  of 
a  soil  pipe  as  shown.  This  chamber  is  arranged  for  absorbing  the 
liquids  and  for  this  purpose  is  provided  with  lengths  of  porous 
tile  radiating  from  the  bottom  as  shown  in  the  plan.  The  house 
drain  connects  with  the  larger  chamber,  which  fills  to  the  level  of 
the  overflow,  .then  the  liquid  portion  of  the  sewage  drains  over 


435 


28 


PLUMBING. 


into  chamber  No.  2  and  is  absorbed  through  the  porous  tile  branches. 
The  solid  part  remains  in  chamber  No.  1,  and  can  be  removed 
from  time  to  time.  A  suitable  trap  should  of  course  be  placed 
in  the  house  drain  in  the  same  manner  as  though  connected  with 
a  street  sewer.  The  safety  of  the  cesspool  will  depend  much  upon 
its  location,  its  general  construction  and  care  and  the  nature  of  the 
soil. 

TRAPS  AND  VENTS. 

Traps.      The    best    method    of    connecting    traps,  and    their 
actual  value  under  all  conditions,  are  matters  upon  which  there  is 


Fig.  63. 

much  difference  of  opinion.  Cities  also  vary  in  their  require- 
ments to  a  greater  or  less  extent,  so  that  it  will  be  possible  to 
show  in  a  general  way  only  the  various  principles  involved  and  to 
illustrate  what  is  considered  good  practice,  in  the  average  case,  at 
the  present  time. 

A  separate  trap  should  in  general  be  placed  in  the  waste  pipe 
from  each  fixture,  although  several  of  a  kind,  such  as  lavatories, 
etc.,  are  often  drained  through  a  common  trap,  as  shown  in  Fig.  64. 

In  addition  to  the  traps  at  the  'fixtures  a  main  or  running 
trap  is  placed  in  the  main  soil  pipe  outside  of  all  the  connections; 


436 


PLUMBING. 


29 


this  is  sometimes  placed  in  a  manhole  just  outside  the  building, 
but  more  commonly  in  the  cellar  before  passing  through  the  wall ; 
the  former  method  is  much  to  be  preferred,  as  the  trap  may  be 
cleaned  without  admitting  gases  or  odors  to  the  house.  The  run- 
ning trap  has  been  shown  in  Fig.  29,  and  is  provided  with  a 
removable  cap  for  cleaning. 

The  agencies  which  tend  to  destroy  the  water  seal  of  traps 


Fig.  04. 

are  siphonage,  evaporation,  back  pressure,  capillary  action,  leakage 
and  accumulation  of  sediment. 

Siphonage.  This  can  best  be  illustrated  by  a  few  simple 
diagrams  showing  the  principles  involved.  In  Fig.  65  is  shown  a 
U  tube  with  legs  of  equal  length  and  filled  with  water.  If  we 


Fig. 


66. 


Fig.  67. 


invert  the  tube,  as  shown  in  Fig.  66,  the  water  will  not  run  out, 
because  the  legs  are  of  equal  length,  and  contain  equal  weights 
of  water,  which  pull  downward  from  the  top  with  the  same  force, 
tending  to  form  a  vacuum  at  the  point  A.  If  one  of  the  legs  is 
lengthened,  as  in  Fig.  67,  so  that  the  column  of  water  is  heavier  on 
one  side  than  on  the  other,  it  will  run  out,  while  atmospheric  pressure 
will  force  the  water  in  the  shorter  tube  up  over  the  bend,  as  there 


437 


30 


PLUMBING. 


would  be  no  pressure  to  resist  this  action  should  the  column  of 
water  break  at  this  point.  This  action  is  also  assisted  by  the 
adhesion  of  the  particles  of  water  to  eacli  other.  The  column  of 
water  in  the  tube  may  be  likened  to  a  piece  of  flexible  rope 
hanging  over  a  pulley;  when  equal  lengths  hang  over  each  side  it 
will  remain  stationary,  but  if  drawn  over  one 
side  slightly,  so  that  one  end  is  heavier  than 
the  other,  the  whole  rope  will  be  drawn  over 
the  pulley  toward  the  longer  and  heavier 
end.  The  first  cause,  due  to  atmospheric 
pressure,  is  the  principal  reason  for  the  action 
of  siphons,  but  the  latter  assists  it  to  some 
extent.  If  the  shorter  leg  of  the  siphon  be 
dipped  in  a  vessel  of  water,  as  shown  in 
Fig.  68,  the  atmospheric  pressure,  which  be- 
fore acted  on  the  bottom  of  the  water  in  the 
tube,  is'  transferred  to  the  surface  of  the 
water  in  the  vessel,  and  the  flow  through  the  tube  will  con- 
tinue until  the  water  level  in  the  vessel  falls  slightly  below  the 
end  of  the  tube  and  admits  air  pressure,  which  breaks  the  siphon 

action.    Fig.  69  shows  the  same  principle      . . 

applied  to  the  trap  of  a  sink  or  bowl. 
If  the  bowl  is  well  rilled  with  water, 
sc  that  when  the  plug  is  removed  from 
the  bottom,  the  waste  pipe  for  some 
distance  below  the  trap  is  filled  with 
a  solid  column  of  water,  a  siphon  action 
will  be  set  up  like  the  one  just  de- 
scribed, and  the  trap  will  be  drained. 
Frequently  a  sufficient  amount  of  water 
runs  down  from  the  fixture  and  sides  of 
the  pipe  above  the  trap  to  partially  re- 
store the  seal.  This  direct  action  of 


Fig.  68. 


Fig.  69. 


the  water  of  a  fixture  in  breaking  its  own  trap  seal  by  siphoning 
is  called  "self-siphonage." 

A  more  common  form,  where  two  or  more  fixtures  connect  with 
the  same  waste  pipe,  is  shown  in  Fig.  70.  In  this  case  the  seal 
of  the  lower  closet  is  broken  by  the  discharge  of  the  upper.  The 


438 


PLUMBING. 


falling  column  of  water  leaves  behind  it  a  partial  vacuum  in  the 
soil  pipe,  and  the  outer  air  tends  to  rush  into  the  pipe  through 
the  way  of  least  resistance,  which  is  often  through  the  trap  seals 
of  the  fixtures  below.  The  friction  of  the  rough  sides  of  a  tall 
soil  pipe,  even  though  it  be  open  at  the  roof,  will  sometimes 
cause  more  resistance  to  air  flow  than  the  trap  seals  of  the  fixtures, 
with  the  result  that  they  are  broken,  and 
gases  from  the  drain  are  free  to  enter  the 
building. 

Three  methods  have  been  employed  to 
prevent  the  destruction  of  the  seal  by  siphon- 
age.  The  first  method  devised  was  what  is 
known  as  "  back  venting,"  and  this  is  largely 
in  use  at  the  present  time,  although  careful 
experiments  have  shown  that  in  many  cases 
it  is  not  as  effective  as  it  was  at  first  sup- 
posed to  be,  and  is  considered  by  some 
authorities  to  be  a  useless  complication.  It 
is,  however,  called  for  in  the  plumbing  regu- 
lations of  many  cities,  and  will  be  taken  up 
briefly  in  connection  with  other  methods. 

Back  Venting.  This  consists  in  con- 
necting a  vent  pipe  at  or  near  the  highest 
part  of  the  trap,  as  shown  in  Fig.  71.  The 
action  of  this  arrangement  is  evident;  in 
place  of  the  waste  pipe  receiving  the  air 
necessary  to  fill  it,  through  the  basin,  after 
the  solid  column  of  water  has  passed  down, 
it  is  drawn  in  through  the  vent  pipe,  as 
shown  by  the  arrows,  and  the  seal  remains,  or  should  remain, 
unbroken.  It  also  prevents  "  self-siphonage "  by  breaking  the 
column  of  water  and  admitting  atmospheric  pressure  at  the 
highest  point  or  crown  of  the  trap.  The  vent  not  only  pre- 
vents the  seal  from  being  broken,  as  described,  but  allows  any 
gases  which  may  form  in  the  waste  pipe  to  escape  above  the  roof 
of  the  house.  In  order  to  be  effective,  the  back  vent  should  be 
large,  but  even  when  of  the  same  size  as  the  waste  pipe,  the  flush- 
ing of  a  closet  will  oftentimes  break  the  seal,  especially  if  the 


Fig.  70. 


439 


32 


PLUMBING. 


vent  pipe  is  of  considerable  length.  The  vent  often  becomes 
choked,  either  with  the  accumulation  of  sediment  near  the  trap  or 
by  frost  or  snow  at  the  top ;  in  this  case  its  effect  is  of  course 
destroyed.  Another  disadvantage  of  the  back  vent  is  the  hasten- 
ing of  evaporation  from  the  trap  and  the  unsealing  of  fixtures 
which  are  not  often  used. 

The  second  method  of  guarding  against  the  loss  of  seal  by 

V 


Fig.  71. 


Fig.  72. 


siphonage  is  to  make  the  body  of  the  trap  so  large  that  a  sufficient 
quantity  of  water  will  always  adhere  to  its  sides  after  siphoning 
to  restore  a  seal.  The  pot  or  cesspool  trap  shown  in  Fig.  72~is 
based  on  this  principle. 

The  third  method  consists  in  the  use  of  a  trap  of  such  form 
that  it  will  not  siphon,  and  will  at  the  same  time  be  self-cleaning. 
Among  other  types  the  centrifugal  trap,  shown  in  Figs.  34  and  35, 
is  claimed  to  fulfil  these  conditions.  The  pot  trap,  while  less 
affected  by  the  siphoning  action,  is  more  or  less  objectionable  on 
account  of  retaining  much  of  the  sediment  and  solid  part  of  the 
sewage  which  falls  into  it. 

Local  Vents.  A  local  vent  is  a  pipe  connected  directly  with 
a  closet  or  urinal  for  carrying  off  any  odor  when  in  use.  It  has 
no  connection  with  the  soil  pipe,  unless  the  trap  seal  becomes 
broken,  and  is  not  provided  for  the  purpose  of  carrying  off  gases 
from  the  sewer.  A  urinal  provided  with  a  local  vent  is  shown  in 
Fig.  73. 

Sometimes  a  small  register  face  back  of  the  fixture,  and  eon- 


440 


PLUMBING. 


necting  with  a  flue  in  the  wall,  is  used  in  place  of  the  regular 
local  vent.  In  order  for  a  vent  flue  of  either  form  to  be  of  any 
value,  it  must  be  warmed  to  insure  a  proper  circulation  01  air 
through  it.  This  is  done  in  some  cases  by  placing  a  gas-jet  at 
the  bottom  of  the  flue,  in  others  a  steam  or  hot  water  pipe  is 
run  through  a  portion  of  the  flue,  and  in  still  others  the  vent 
is  carried  up  beside  a  chimney  flae,  from  which  it  may  receive 
sufficient  warmth  to  assist  the  circulation  to  some  extent. 

Main  or  Soil  Pipe  Vent.  It 
is  customary  to  vent  the  main  soil 
pipe  by  carrying  it  through  the 
roof  of  the  building,  and  leaving 
the  end  open.  This  is  shown  in 
Fig.  74.  On  gravel  roofs  which 
drain  toward  the  center,  the  soil 
pipe  is  sometimes  stopped  on  a 
level  with  the  roof,  and  serves  as 
a  rain  leader.  In  other  cases  the 
roof  water  may  be  led  to  the  soil 
pipe  in  the  cellar.  If  the  latter 
method  is  used,  the  water  should 
pass  through  a  deep  trap  before 
connecting  with  the  drain.  These 
arrangements  tend  both  to  flush 
out  the  soil  pipe  and  "trap  and 
prevent  the  accumulation  of  sedi- 
ment. 

Fresh  Air  Inlets.  The  fresh  air  inlet  shown  just  above  the  run- 
ning trap  Fig.  74  is  to  cause  a  circulation  of  air  through  the  soil 
pipe,  as  shown  by  the  arrows.  The  connection  should  be  made  just 
inside  of  the  trap,  so  that  the  entire  length  of  the  drain  will  be 
swept  by  the  current  of  fresh  air.  It  is  sometimes  advised  to 
extend  the  fresh  air  pipe  up  to  the  roof,  because  foul  air  may  at 
times  be  driven  out  by  heavy  flushing  of  the  drain  pipe,  but  where 
this  is  done  there  is  much  less  chance  for  circulation,  as  the  inlet 
and  outlet  are  nearly  on  a  level,  and  the  columns  of  air  in  them 
are  more  likely  to  be  balanced.  By  carrying  the  inlet  six  or  eight 
feet  above  the  ground  both  objections  are  overcome  to  some  extent, 


Fig.  73. 


441 


PLUMBING. 


unless  this  brings  it  near  a  window,  which,  of  course,  would  not 
be  safe.  The  main  trap  does  not  require  a  back  vent,  for  should 
it  be  siphoned  under  ordinary  conditions,  it  will  always  be  filled 


Fig.  74. 

again  within  a  few  minutes;  and  if  the  main  soil  pipe  is  open  at 
the  top  and  all  fixtures  are  properly  tapped,  no  harm  would  come 
from  the  slight  leakage  of  gas  into  the  drain  under  these  condi- 


442 


NICKEL    PLATED    BRASS    SHOWER    BATH. 

The  Federal  Company. 


PLUMBING.  35 


tions,  and  some  engineers  recommend  the  omission  of  the  running 
trap. 

Where  a  house  drains  into  a  cesspool  instead  of  a  sewer,  it  is 
far  more  necessary  that  the  system  should  be  trapped  against  it 
as  it  gives  off  a  constant  stream  of  the  foulest  gases.  The  usual 
form  of  running  trap  serves  to  protect  the  house,  but  the  cesspool 
should  have  an  independent  vent  pipe  leading  to  some  unobjection- 
able point  and  carried  well  up  above  the  surface  of  the  ground. 

Disposal  of  Sewage.  In  cities  and  towns  having  a  system 
of  sewers,  or  where  there  is  a  large  stream  of  running  water  near 
by,  the  matter  is  a  simple  one.  In  the  first  case,  the  house  drain 
is  merely  extended  to  the  sewer,  into  which  it  should  discharge  at 
as  high  a  point  as  possible,  and  at  an  acute  angle  with  the  direction 
of  flow.  When  the  drain  connects  with  a  stream  it  should  be 
carried  out  some  distance  from  the  shore  and  discharge  under 
water,  an  opening  for  ventilation  being  provided  at  the  bank. 
Where  there  are  neither  sewers  nor  streams,  the  cesspool  must  be 
used.  When  the  soil  is  sufficiently  porous  the  method  shown  in 
Fig.  63  may  be  employed.  Sometimes  the  sewage  is  collected  in 
a  closed  cistern  and  discharged  periodically  through  a  flush  tank 
into  a  series  of  small  tiles  laid  to  a  gentle  grade,  from  8  to  12 
inches  below  the  surface.  By  extending  these  tiles  over  a  sufficient 
area  and  allowing  from  40  to  70  feet  of  tile  for  each  person,  a 
complete  absorption  of  the  sewage  takes  place  by  the  action  of  the 
atmosphere  and  the  roots. 

PIPE  CONNECTIONS. 

The  Bath  Room.  There  are  different  methods  of  connect- 
ing up  the  fixtures  in  a  bath  room,  depending  upon  the 
general  arrangement,  type,  the~kind  of  trap  used,  etc.  Fig.  75 
shows  a  set  of  fixtures  connected  up  with  vented  traps.  Both  the 
soil  and  vent  pipes  are  carried  above  the  roof  with  open  ends. 
No  trap  or  fixture  should  be  vented  into  a  chimney,  as  is  quite 
commonly  done ;  this  may  work  satisfactorily  when  the  flues  are 
warm,  but  in  summer  time,  when  the  fires  are  out,  there  are  quite 
likely  to  be  down  drafts,  which  cause  the  gases  to  be  carried  into 
the  vooms  through  stoves  or  fireplaces.  The  vent  pipe,  although 
usually  carried  through  the  roof  independently,  is  sometimes 


443 


36 


PLUMBING. 


connected  with  the  soil  pipe  above  the  highest  fixture  ;  the  soil 
pipe  is  often  made  a  larger  size  through  the  attic  space  and  above 
the  roof  in  order  to  increase  the  upward  tlow  of  air  through  it. 
Fig.  76  shows  a  set  of  bath  room  connections  in  which  non-siphon- 
ing traps  are  used  without  back  venting  ;  this  is  a  simpler  and  less 
expensive  method  of  making  the  connections  and  is  especially 
recommended  by  some  engineers.  Its  efficiency  of  course  depends 
upon  the  proper  working  of  the  traps. 


Fij?.  75. 

The  bath  room  itself  should  be  well  lighted,  and  if  possible, 
in  a  location  where  it  will  receive  the  sun.  It  should  be  arranged 
so  that  it  may  be  heated  to  a  higher  temperature  than  other  rooms 
in  the  house  if  desired,  and  it  should  also  be  thoroughly  ventilated, 
the  vent  register  being  placed  5  or  6  feet  above  the  floor  in  order 
that  it  may  carry  off  any  steam  which  rises  from  the  bath  tub. 
The  walls,  doors,  etc.,  should  be  finished  in  a  way  to  make  them 
as  nearly  waterproof  as  possible  ;  some  form  of  good  enamel  paint 
answers  well  for  this  purpose.  Paper  should  never  be  used  on 
the  walls,  nor  carpets  on  the  floors,  which  should  be  of  hard  wood. 
Where  the  ^xpense  is  not  a  matter  of  importance,  glazed  tile  may 
be  used  for  the  floor  and  walls.  Means  should  always  be  provided 


444 


PLUMBING. 


for  ventilating  the  bathroom  without  opening  the  door  into  the 

other  rooms,  and  the  greatest  care  should  be  taken  to  keep  not 

only  the  fixtures,  but  the  room  itself,  in  the  most  perfect  order. 

Urinal  Connections.     The  common  form  of  urinal  connection 


Fig.  76. 

is  shown  in  Fig.  14.  The  overflow  from  the  trap  ends  in  a  tee, 
the  lower  outlet  of  which  connects  with  the  soil  pipe  and  the 
upper  with  the  vent  pipe.  Where  several 
urinals  are  erected  side  by  side  it  is  usual  to 
omit  the  individual  traps,  using  the  direct 
outlet  connection  shown  in  Fig.  77.  These 
connect  with  a  common  waste  pipe  and  drain 
through  a  single  trap  to  the  soil  pipe. 

Kitchen  Sink  Connections.  Fig.  78 
shows  the  usual  method  of  making  the  con- 
nections for  a  kitchen  sink.  The  waste  and 
vent  are  of  lead,  connected  with  the  main 
cast-iron  soil  and  vent  pipes  by  means  of 
brass  ferules  and  wiped  joints. 

Soil  and  Waste  ^Pipes.  The  various  fixtures  have  been 
taken  up,  together  with  the  different  kinds  of  traps  which  are  used 
in  connection  with  them,  and  also  the  general  methods  of  making 
the  various  connections  for  waste  and  vent.  We  will  next  take 


Fig.  77. 


445 


38 


PLUMBING. 


up  some  of  the  points  in  regard  to  the  manner  of  running  and 
supporting1  the  different  pipes,  together  with  the  proper  sizes  to  he 
used  under  different  conditions. 

The  waste  pipes  of  necessity  contain  more  foul  matter  and 
therefore  more  harmful  gases  than  the  fixtures,  so  that  especial 
care  must  be  taken  in  their  arrangement  and  construction.  It  is 
advisable  to  keep  all  piping  as  simple  as  possible,  using  as  few 
connections  as  is  consistent  with  the  proper  working  of  the 
system. 

The  fixtures  on  each  floor  should  be  arranged  to  come  directly 
over  each  other,  so  as 
to  avoid  the  running  of 
horizontal  pipes  across  or 
between  the  floor  beams. 
The  sizes  of  pipes  com- 
monly used  require  such 
a  sharp  grade  that  there 
is  not  sufficient  space, 
in  ordinary  building  con- 
struction, between  the 
floor  boards  and  ceiling 
lath  below  for  horizontal 
runs  of  much  length. 
One  soil  pipe  is  usually 
sufficient  for  buildings 
of  ordinary  size,  and  in 
cold  climates  is  nec- 
essarily carried  down  inside  the  building  to  prevent  freezing. 
One  or  more  waste  pipes  from  sinks,  bathtubs,  etc.,  are  usually 
required  in  addition  to  the  soil  pipe  These  may  be  connected 
directly  with  the  soil  pipe  (through  traps),  if  located  near  it,  or 
may  be  carried  to  the  basement  vertically  and  then  joined  with 
the  main  drain  pipe  inside  the  running  trap.  These  should  also 
be  placed  on  the  inside  wall  of  the  house,  and,  if  necessary  to 
conceal  them,  the  boxing  used  should  be  put  together  in  such  a 
manner  that  it  may  be  easily  removed  for  inspection. 

The  main   soil  pipe  should  also  be  placed  where  it  can  be 


446 


PLUMBING. 


seen,  so  that  leaks  may  be  easily  discovered ;  it  is  commonly  run 
along  the  basement  wall  and  supported  by  suitable  brackets  or 
hangers.  If  carried  beneath  the  cellar  floor,  it  should  run  in  a 
brick  trench  with  removable  covers.  In  running  all  lines  of  pipe, 
whether  vertical  or  horizontal,  they  should  be  securely  supported 
and,  in  the  case  of  the  latter,  properly  graded.  Some  of  the 
various  kinds  of  hangers  and  supports  used  are  shown  in  Figs.  79 
and  80.  The  grade  of  the  pipes  should  be  as  sharp  and  as  uniform 
as  possible.  The  velocity  in  the  pipes  should  be  at  least  two  feet 
per  second  to  thoroughly  clean  them  and  prevent  clogging.  Gen- 
erally speaking,  the  pitch  of  the  pipes  should  not  be  in  any  case 
less  than  1  foot  in  50.  In  running  lines  of  soil  pipe,  it  is  best  to 


Fig.  79.  Fig.  80. 

set  the  joints  ready  for  calking  in  the  exact  positions  they  are' 
to  occupy  and  resting  upon  the  supports  which  are  intended  to 
hold  them  permanently.  In  this  way  there  is  less  liability  of  sag- 
ging or  loosening  of  the  joints  after  calking.  In  the  running  of 
vertical  pipes,  care  should  be  taken  to  have  them  as  straight  as 
possible  from  the  lowest  fixture  to  the  roof. 

It  is  very  necessary  that  the  pipes  be  given  such  an  align- 
ment that  the  water  entering  them  will  meet  with  no  serious 
obstructions.  Where  vertical  pipes  join  those  which  are  horizon- 
tal, they  should  be  given  a  bend  which  will  turn  the  stream  gradu- 
ally into  the  latter,  thus  preventing  any  resistance  and  the  result- 
ing accumulation  of  deposits.  Horizontal  pipes  may  be  joined 
with  vertical  pipes  without  a  bend,  as  the  discharge  will  be  suffi- 
ciently free  without  it.  However,  it  is  customary  to  use  a  Y  or 
T  branch,  giving  a  downward  direction  to  the  flow  when  connect- 
ing a  closet  or  other  fixture  where  there  is  likely  to  be  much  solid 
matter  in  the  sewage.  Offsets  should  always  be  avoided  as  far 
as  possible,  as  they  obstruct  the  flow  of  both  water  and  air. 


447 


40  PLUMBING. 


Pipe  Sizes.  The  most  importer t  requirements  in  the  case 
of  discharge  pipes  are  that  they  cany  away  the  waste  matter  as 
thoroughly  as  possible  without  stoppage  of  flow  or  eddying,  and 
that  they  be  well  ventilated.  In  order  to  accomplish  this  they 
must  be  given  such  sizes  as  experience  has  shown  to  be  the  best. 
When  water  having  solid  matter  in  suspension  half  fills  a  pipe,  the 
momentum  or  force  for  clearing  the  pipe  will  be  much  greater  than 
when  it  forms  only  a  shallow  stream  in  one  of  a  larger  size,  so  that 
in  proportioning  the  suas  of  soil  pipes  and  drains  care  must  be 
taken  that  they  are  no',,  made  larger  than  necessary,  for  if  the 


Fig.  81. 

stream  becomes  too  shallow  the  pipes  will  not  be  properly  flushed 
and  deposits  are  likely  to  accumulate.  The  amount  of  water  used 
in  a  house  of  ordinary  size,  even  wrhen  increased  by  the  roof  water 
from  a  heavy  rain,  will  easily  be  cared  for  by  a  4-inch  pipe  having 
a  good  pitch.  While  a  pipe  of  this  size  would  seem  to  be  sufficient, 
it  is  found  by  experience  that  it  is  likely  to  become  clogged  at 
times  by  substances  which  through  carelessness  find  their  way  into 
the  drain,  so  that  it  seems  best  to  use  a  somewhat  lai-ger  size. 
For  city  buildings  in  general,  it  is  recommended  that  the  main 
drain  should  not  be  less  than  5  or  6  inches  in  diameter,  and  in 
ordinary  dwelling  houses  not  less  than  5  inches.  The  vertical 
soil  pipes  need  not  be  larger  than  4  inches,  except  in  very  high 
buildings. 

Waste  pipes  may  vary  from  li  inches  to  2  inches.  The 
waste  from  a  single  bowl  or  lavatory  should  be  1|  inches  in 
diameter,  from  a  bathtub,  kitchen  sink  or  laundry  tub  1  *  inches, 
from  a  slop  sink  1|  inches.  Smaller  pipes  should  never  be  used. 
In  laying  out  the  lines  of  piping,  provision  should  be  made  for 
clearing  the  pipes  in  case  of  stoppage.  Fig.  81  shows  how  this 


448 


PLUMBING. 


41 


may  be  done.  Clean-out  plugs  are  left  at  the  points  indicated  by 
the  arrows,  so  that  flexible  sticks  or  strips  of  steel  may  be  inserted 
to  dislodge  any  obstruction  which  may  occur. 

The  fresh-air  inlet  to  the  main  drain  pipe  has  already  been 
referred  to.  This  should  be  located  away  from  windows,  where 
foul  air  would  be  objectionable ;  in  cities  they  may  be  placed 
at  the  curb  line  and  covered  with  a  grating.  Sometimes 
they  are  arranged  as  shown  in 
Fig.  82.  The  opening  is  made 
in  the  usual  way,  and  a  hood 
placed  over  the  inlet,  and  a  pipe 
leading  from  this  is  carried 
through  the  roof.  When  the 
circulation  of  air  is  upward 
through  the  main  soil  pipe  the 
opening  acts  in  the  usual  way, 
that  is,  as  a  fresh-air  inlet,  but 
should  there  be  a  reversal  of 
the  current  from  any  reason, 
which  would  discharge  foul  air 
from  the  sewer,  it  would  be 
caught  by  the  overhanging 

hood  and  carried  upward  through  the  connecting  vent  pipe  to  a 
point  above  the  roof.  A  general  layout  for  house  drainage  is 
shown  in  Fig.  83. 

PLUMBING  FOR  VARIOUS  BUILDINGS. 

Dwelling  Houses.  The  bathroom  fixtures,  laundry  tubs  and 
kitchen  sink,  with  the  possible  addition  of  a  slop  sink,  make  up  the 
usual  fixtures  to  be  provided  for  in  the  ordinary  dwelling  house. 
In  houses  of  larger  size  these  may  be  duplicated  to  some  extent, 
but  the  general  methods  of  connection  are  the  same  as  have  already 
been  described  and  need  not  be  taken  up  again  in  detail. 

Apartment  Houses.  These  are  usually  made  up  of  duplicate 
flats,  one  above  the  other,  so  that  the  plumbing  fixtures  may  be  the 
same  for  each.  It  is  customary  to  place  the  bathrooms  in  the 
same  position  on  each  floor,  so  that  a  single  soil  pipe  will  care  for 
all. 


449 


PLUMBING. 


Hotels.  Here,  as  in  the  case  just  described,  the  bathrooms 
are  placed  one  above  another,  so  that  a  single  soil  pipe  may  care 
for  each  series,  and  the  problem  then  becomes  that  of  duplicat- 
ing the  layout  for  an  apartment  house.  In  addition  to  the 
private  baths  there  is  a  public  lavatory  or  toilet-room,  usually  on 
the  first  floor  or  in  the  basement.  T  as  is  fitted  up  with  closets, 


urinals  and  bowls.  The  closet  seats  and  urinals  are  placed  side 
by  side,  with  dividing  partitions,  and  connect  with  a  common  soil 
pipe  running  back  of  them  and  having  a  good  pitch.  Each  fixture 
should  have  its  own  trap.  The  flushing  of  the  fixtures  is  often 
made  automatic,  so  that  pressing  down  the  wooden  rim  of  a  closet 


450 


PLUMBING. 


seat  will  throw  a  lever  which  on  being  released  will  flush  the 
closet.  Urinals  are  commonly  made  to  flush  at  regular  intervals 
by  some  of  the  devices  already  shown.  The  lavatories  are  made 
up  in  long  rows,  as  shown 
in  Fig.  84. 

Railroad  Stations.  The 
plumbing  of  a  railroad 
station  is  similar  to  that 
of  a  hotel,  although  even 
greater  care  should  be 
taken  to  make  the  fixtures 
self-cleansing,  as  the 
patrons  are  likely  to  in- 
clude many  of  the  lowest 
and  most  ignorant  class  of 
people.  Special  attention 
should  be  given  to  both 
the  local  ventilation  of  the 
fixtures  and  the  general 
ventilation  of  the  room. 

Schoolhouses.  The 
same  general  rules  hold  in 
the  case  of  school  buildings 
as  in  hotels  and  railroad 
stations.  As  the  pupils 
are  under  the  direct  super- 
vision of  teachers  and  jani- 
tors it  is  not  necessaiy  to 
have-  the  fixtures  auto- 
matic to  as  great  an  extent 
as  in  the  cases  just  de- 
scribed, and  it  is  customary 
to  flush  the  closets  by 
means  of  tanks,  and  pull 
chains  or  rods,  the  same  as  in  private  dwellings.  The  urinals 
may  be  automatic  or  a  small  stream  of  water  may  be  allowed 
to  flow  through  them  continuously  during  school  hours.  A  good 
form  for  this  class  of  work  is  shown  in  Fig.  85. 


451 


44 


PLUMBING. 


Shops  and  Factories.      Some  simple    type  of  fixture  which 
can  be  easily  sared  for  is  best  in  buildings  of  this  kind. 


TESTING  AND  INSPECTION. 


All  plumbing  work  of  any  importance  should  be  given  two 
tests ;  the  first,  called    the  "  roughing  test,"  applies  only  to  the 


452 


PLUMBING.  45 


soil,  waste  and  vent  pipes,  and  is  made  before  the  fixtures  are 
connected.  The  best  method  of  making  this  test  is  to  plug  the 
main  drain  pipe  just  outside  the  running  trap,  and  also  all  open- 
ings for  the  connections  of  fixtures,  etc.,  and  then  fill  the  entire 
system  with  water.  This  may  be  done  in  small  systems  through 
the  main  vent  pipe  on  the  roof,  and  in  larger  ones  by  making  a 
temporary  connection  with  the  water  main.  If  any  leaks  are 
present  they  are  easily  detected  in  this  way.  In  cold  weather, 
when  there  would  be  danger  of  freezing,  compressed  air  under  a 
pressure  of  at  least  ten  pounds  per  square  inch  may  be  used  in 
place  of  water.  Leaks  in  this  case  must  be  located  by  the  sound 
of  the  issuing  air.  The  water  test  is  to  be  preferred  in  all  cases, 
as  it  is  easier  to  make,  and  small  leaks  are  more  easily 
detected. 

The  final  test  is  made  after  the  fixtures  are  in  and  all  work 
is  completed.  There  are  two  ways  of  making  this  test,  one  known 
as  the  "peppermint  test,"  and  the  other  as  the  "smoke  test."  In 
making  either  of  these,  the  system  should  first  be  flushed  with 
water,  so  that  all  traps  may  be  sealed.  If  peppermint  is  used,  4 
to  6-ounces  of  oil  of  peppermint,  depending  upon  the  size  of  the 
system,  are  poured  down  the  main  vent  pipe,  and  then  a  quart  or 
two  of  hot  water  to  vaporize  the  oil.  The  vent  pipe  is  then 
closed,  and  the  inspector  must  carefully  follow  along  the  lines  of 
piping  and  locate  any  leaks  present  by  the  odor  of  the  escaping 
gas.  Another  and  better  way  is  to  close  the  vent  pipe  and 
vaporize  the  oil  in  the  receiver  of  a  small  air  pump,  and  then 
force  the  gas  into  the  system  under  a  slight  pressure.  The  re- 
ceiver is  provided  with  a  delicate  gage,  so  that  after  reaching  a 
certain  pressure  (which  must  not  be  great  enough  to  break  the 
trap  seals)  the  pump  may  be  stopped  and  the  pressure  noted.  If, 
after  a  short  time,  the  pressure  remains  the  same,  it  is  known  that 
the  system  is  tight ;  if,  however,  the  pressure  drops,  then  leaks 
are  present  and  must  be  located,  as  already  described.  Ether  is 
sometimes  used  in  place  of  peppermint  for  this  purpose. 

In  making  the  smoke  test  the  system  is  sealed,  and  the  vent 
pipes  closed  in  the  same  manner  as  for  the  test  just  described; 
smoke  from  oily  waste  or  some  similar  substance  is  then  forced 
into  the  pipes  by  means  of  a  bellows.  When  the  system  is  filled 


453 


46  PLUMBING. 


with  smoke,  and  a  slight  pressure  produced,  the  fact  is  shown  by 
a  iloafc,  which  rises  and  remains  in  this  position  if  the  joints  are 
tight.  If  there  are  leaks,  the  float  falls  as  soon  as  the  bellows 
are  stopped.  Leaks  may  be  detected  in  this  way,  both  by  the 
odor  of  the  smoke  and  by  the  issuing  jets  from  leaks  of  any  size. 
Special  machines  are  made  for  both  the  peppermint  and  smoke  tests. 
The  water  test  is  preferable  for  roughing  in,  and  the  smoke 
test  for  the  final.  Every  system  of  plumbing  should  be  tested  at 
least  once  a  year. 

SEWERAGE  AND  SEWAGE  PURIFICATION. 

An  abundant  supply  of  pure  water  is  a  necessity  in  every  town 
and  city ;  and  such  a  supply  having  been  secured  brings  up  the 
question  of  its  disposal  after  being  used.  This  is  plainly  the  re- 
verse of  its  introduction.  As  it  was  distributed  through  a  net- 
work of  conduits,  diminishing  in  size,  with  its  numerous  branches, 
so  it  may  be  collected  again  by  similar  conduits,  increasing  in  size, 
as  one  after  another  they  unite  in  a  common  outlet. 

This  fouled  water  is  called  seivage,  and  the  conduits  which  col- 
lect it  constitute  a  sewerage  system.  In  general,  sewage  is  dis- 
posed of  in  two  ways  ;  either  it  must  be  turned  into  a  body  of 
water  so  large  as  to  dilute  it  beyond  all  possibility  of  offence, 
and  where  it  cannot  endanger  human  life  by  polluting  a  public 
water-supply,  or  it  must  be  purified  in  some  manner. 

The  conduits  which  carry  water  collected  from  street  surfaces 
during  and  after  rains,  or  ground  water  collected  from  beneath 
the  surface,  are  called  drains.  When  one  set  of  conduits  removes 
sewage  and  another  carries  surface  and  ground  water,  it  is  said 
that  the  separate  system  of  sewerage  is  in  use.  Where  one  system 
conveys  both  sewage  and  drainage  water  it  is  called  the  combined 
system.  Various  modifications  of  these  two  systems  are  possible, 
both  for  whole  cities  and  for  limited  areas  within  the  same  town 
or  city. 

A  sanitary  sewerage  system  cannot  be  installed  until  a  public 
water-supply  has  been  provided.  It  is  needed  as  soon  as  that  is 
accomplished,  for  while  the  wells  can  then  be  abandoned  the  volume 
of  waste  water  is  greatly  increased  by  the  water-works  system.  Its 
foulness  is  also  much  increased  through  the  introduction  of  water- 


454 


PLUMBING.  47 


closets.  Without  sewers  and  with  a  public  water-supply  cesspools 
must  be  used,  and  with  these  begins  a  continuous  pollution  of  the 
soil  much  more  serious  than  that  which  commonly  results  from 
closets  and  the  surface  disposal  of  slops. 

Among  the  data  which  should  first  be  obtained  in  laying  out 
a  sewerage  system  are : 

First. — The  area  to  be  served,  with  .its  topography  and  the 
general  character  of  the  soil. —  A  contour  map  of  the  whole  town 
or  city,  showing  the  location  of  the  various  streets,  streams,  ponds 
or  lakes,  and  contour  lines  for  each  5  feet  or  so  of  change  in  ele- 
vation, is  necessary  for  the  best  results.  The  general  character  of 
the  soil  can  usually  be  obtained  by  observation  and  inquiry  among 
residents  or  builders  who  have  dug  wells  or  cellars,  or  have  ob- 
.jerved  work  of  this  kind  which  was  being  done.  The  kind  of 
soil  is  important  as  affecting  the  cost  of  trenching  and  its  wetness 
or  dryness,  and  this,  together  with  a  determination  of  the  ground- 
water  level,  will  be  useful  in  showing  the  extent  of  underdraining 
necessary. 

Second. — Whether  the  separate  or  combined  system  of  sewer- 
age, or  a  compromise  between  the  two  is  to  be  adopted. —  These 
points  will  depend  almost  wholly  upon  local  conditions.  The  size 
and  cost  of  combined  sewers  is  much  greater  than  the  separate 
system,  since  the  surface  drainage  in  times  of  heavy  rainfall  is 
many  times  as  great  as  the  flow  of  sanitary  sewage.  In  older 
towns  and  cities  it  sometimes  happens  that  drains  for  removing' 
the  surface  water  are  already  provided,  and  in  this  case  it  is  only 
necessary  to  put  in  the  sanitary  sewers ;  or  again,  the  latter  may 
be  provided,  leaving  the  matter  of  surface  drainage  for  future  con- 
sideration. 

If  the  sewage  must  be  purified,  the  combined  system  is  out 
of  the  question,  for  the  expense  of  treating  the  full  flow  in  times 
of  maximum  rainfall  would  be  enormous.  Sometimes  more  or  less 
limited  areas  of  a  town  may  require  the  combined  system,  while 
the  separate  system  is  best  adapted  to  the  remainder ;  and  again 
it  may  be  necessary  to  take  only  the  roof  water  into  the  sewers. 
As  already  stated,  local  conditions  and  relative  costs  are  the 
principal  factors  in  deciding  between  the  separate  and  combined 
systems. 


455 


48  PLUMBING. 


Third. —  Whether  subsoil  drainage  shall  be  provided.---  In 
most  cases  this  also  will  depend  upon  local  conditions.  It  is  al- 
ways an  advantage  to  lower  the  ground-water  level  in.  places 
where  it  is  sufficiently  high  to  make  the  ground  wet  at  or  near  the 
surface  during  a  large  part  of  the  year.  In  addition  to  rendering 
the  soil  dry  around  and  beneath  cellars,  the  laying  of  uuderdrains 
is  of  such  aid  in  sewer  .construction  as  to  warrant  their  introduc- 
tion for  this  purpose  alone.  This  is  the  case  where  the  trenches 
are  so  wet  as  to  render  the  making  and  setting  of  cement  joints 
difficult.  The  aim  in  ail  good  sewer  work  is  to  reduce  the  infil- 
tration of  ground  water  into  the  pipes  to  the  smallest  amount; 
but  in  very  wet  soil,  tight  joints  can  be  made  only  with  difficulty, 
and  never  with  absolute  certainty.  Cases  have  beon  known  where 
fully  one-half  the  total  volume  of  sewage  discharged  consisted  of 
ground  water  which  had  worked  in  through  the  joints. 

Fourth. —  The  best  means  for  the  final  disposal  of  the 
sewage. —  Until  recently  it  was  turned  into  the  nearest  river  or 
lake  where  it  could  be  discharged  with  the  least  expense.  The 
principal  point  to  be  observed  in  the  disposal  of  sewage  is  that 
no  public  water-supply  shall  be  endangered.  At  the  present  time 
no  definite  knowledge  is  at  hand  regarding  the  exact  length  of 
time  that  disease  germs  from  the  human  system  will  live  in  water. 
The  Massachusetts  legislature  at  one  time  said  that  no  sewer 
should  discharge  into  a  stream  within  20  miles  of  any  point  where 
it  is  used  for  public  water-supply,  but  it  is  now  left  largely  in  the 
hands  of  the  State  Board  of  Health.  There  may  be  cases  where 
sewage  disposal  seems  to  claim  preference  to  water  supply  in  the 
use  of  a  stream,  but  each  case  must  be  decided  on  its  own  merits. 
Knowing  the  amount  of  water  and  the  probable  quantity  and 
character  of  the  sewage,  it  is  generally  easy  to  determine  whether 
all  of  the  crude  sewage  of  a  city  can  safely  be  discharged  into  the 
bodj'  of  water  in  question.  Averages  in  this  case  should  never 
be  used;  the  water  available  during  a  hot  and  dry  summer,  when 
the  stream,  or  lake  is  at  its  lowest,  and  the  banks  and  beds  are  ex- 
posed to  the  sun,  is  what  must  be  considered.  Where  sewage  is 
discharged  into  large  bodies  of  water,  either  lakes  or  the  ocean,  it 
is  generally  necessary  to  make  a  careful  study  of  the  prevailing 
currents  in  order  to  determine  the  most  available  point  of  discharge, 


456 


PLUMBING.  49 


in  order  to  prevent  the  sewage  becoming  stagnant  in  bays,  or  the 
washing  ashore  of  the  lighter  portions.  Such  studies  are  com- 
monly made  with  floats,  which  indicate  the  direction  of  the  exist- 
ing currents. 

Fifth. —  Population,  water  consumption  and  volume  of  sewage 
for  which  provision  should  be  made,  together  with  the  rainfall 
data,  if  surface  drainage  is  to  be  installed. — The  basis  for  population 
studies  is  best  taken  from  the  census  reports,  extending  back  many 
years.  By  means  of  these  the  probable  growth  may  be  estimated 
for  a  period  of  from  30  to  50  years.  In  small  and  rapidly  grow- 
ing towns  it  must  be  remembered  that  the  rate  of  increase  is  gen- 
erally less  as  the  population  becomes  greater. 

It  is  desirable  to  design  a  sewerage  system  large  enough  to 
serve  for  a  number  of  years,  20  or  30  perhaps,  although  some 
parts  of  the  work,  such  as  pumping  or  purification  works,  may 
be  made  smaller  and  increased  in  size  as  needed. 

The  pipe  system  should  be  large  enough  at  the  start  to  serve 
each  street  and  district  for  a  long  period,  as  the  advantages  to  be 
derived  from  the  use  of  city  sewers  are  so  great  that  all  houses 
are  almost  certain  to  be  connected  with  them  sooner  or  later.  It 
is  often  necessary  to  divide  a  city  into  districts  in  making  esti- 
mates of  the  probable  growth  in  population.  Thus  the  residential 
sections  occupied  by  the  wealthiest  classes  will  be  comprised  of  a 
comparatively  small  population  per  acre,  due  to  the  large  size  of 
the  lots.  The  population  will  grow  more  dense  in  the  sections 
occupied  by  the  less  wealthy,  the  well-to-do  and  finally  the  tene- 
ment sections.  In  manufacturing  districts  the  amount  of  sewage 
will  vary  somewhat,  depending  upon  the  lines  of  industry 
carried  on. 

The  total  water  consumption  depends  mainly  upon  the  popu- 
lation, but  no  fixed  rule  can  be  laid  down  for  determining  it 
beforehand.  It  is  never  safe  to  allow  less  than  60  gallons  per 
day  per  capita  as  the  average  water  consumption  of  a  town  if 
most  of  the  people  patronize  the  public  water-supply.  In  general 
it  is  safer  to  allow  100  gallons.  The  total  daily  flow  of  sewage  is 
not  evenly  distributed  through  the  24  hours.  The  actual  amount 
varies  widely  during  different  hours  of  the  day.  In  most  towns 
there  should  be  little  if  any  sewage,  if  the  pipes  are  tight  enough 


457 


50  PLUMBING. 


to  prevent  inward  leakage,  between  about  10  o'clock  in  the 
evening  and  4  in  tbe  morning.  From  |  to  ?  of  the  daily  flow 
usually  occurs  in  from  9  io  12  hours,  the  particular  hours  varying 
in  different  communities.  This  is  not  of  importance  in  designing 
the  pipe  system,  but  only  affects  the  disposal. 

Rainfall  data  is  usually  hard  to  obtain  except  in  the  cities 
and  larger  towns.  In  cases  of  this  kind  the  data  of  neighboring 
town  or  cities  may  be  used  if  available.  Monthly  or  weekly 
totals  are  of  little  value,  as  it  is  necessary  to  provide  for  the 
heaviest  rains,  as  a  severe  shower  of  15  minutes  may  cause  more 
inconvenience  and  damage,  if  the  sewers  are  not  sufficiently  large, 
than  a  steady  rain  extending  over  a  day  or  two.  A  maximum 
rate  of  1-inch  per  hour  will  usually  cover  all  ordinary  conditions. 
The  proportion  which  will  reach  the  sewers  during  a  given  time 
will  depend  upon  local  conditions,  such  as  the  slope  of  land, 
whether  its  surface  is  covered  with  houses  and  paved  streets, 
cultivated  fields  or  forests,  etc. 

Sixth. —  Extent  and  cost  of  the  proposed  system. —  This  is  a 
matter  largely  dependent  upon  the  local  treasury,  or  the  willing- 
ness of  the  people  to  pay  general  taxes  or  a  special  assessment 
for  the  benelits  to  be  derived. 

DESIGN  AND  CONSTRUCTION. 

The  first  step  is  to  lay  out  the  pipe  or  conduit  system.  For 
this  the  topographical  map  already  mentioned  will  be  found 
useful.  This,  however,  should  be  supplemented  by  a  profile  of  all 
the  streets  in  which  sewers  are  to  be  laid,  in  order  to  determine 
the  proper  grades.  In  laying  out  the  pipe  lines,  special  diagrams 
and  tables  which  have  been  prepared  for  this  purpose  may  be 
used.  In  the  separate  system  it  is  generally  best  to  use  8"  pipe 
as  the  smallest  size  to  lessen  the  risk  of  stoppage,  although  6" 
pipe  is  ample  for  the  volume  of  sanitary  sewage  from  an  ordinary 
residence  street  of  medium  length.  Pipe  sewers  are  generally 
made  of  vitrified  clay,  with  a  salt-glazed  surface.  Cement  pipe  is 
also  used  in  some  cities.  The  size  of  pipe  sewers  is  limited  to 
30  inches  in  diameter,  owing  to  the  difficulty  and  expense  of 
making  the  larger  pipe  and  the  comparative  ease  of  laying  brick 
sewers  of  anv  size  from  24  or  30  inches  up.  In  very  wet  ground, 


458 


COMBINED    NEEDLE    AND    SHOWER    BATH    ARRANGED    FOR    HOT    AND    COLD    WATER. 

The  Federal  Company. 


PLUMBING.  51 


cast  iron  pipe  with  lead  joints  is  used,  either  to  prevent  inward 
leakage  or  settling  of  the  pipe. 

The  pipes  should  be  laid  to  grade  with  great  care  and  a  good 
alignment  should  be  secured.  Hole's  should  be  dug  for  the  bells 
of  the  pipe,  so  that  they  will  have  solid  bearings  their  entire 
length.  If  rock  is  encountered  in  trenching,  it  will  be  necessary 
to  provide  a  bed  for  the  pipe  which  will  not  be  washed  into  fis- 
sures by  the,  stream  of  subsoil  water  which  is  likely  to  follow  the 
sewer  when  the  ground  is  saturated. 

Underdrains.  Where  sewers  are  in  wet  sand  or  gravel, 
underdrains  may  be  laid  beneath  or  alongside  the  sewer.  These 
are  usually  the  ordinary  agricultural  tiles,  from  3  inches  in 
diameter  upward.  They  have  no  joints,  being  simply  hollow 
cylinders,  and  are  laid  with  their  ends  a  fraction  of  an  inch 
apart,  wrapped  with  a  cheap  muslin  cloth  to  keep  out  the  dirt 
until  the  matter  in  the  trench  becomes  thoroughly  packed  about 
them.  These  drains  may  empty  into  the  nearest  stream,  provided 
it  is  not  used  for  a  public  water-supply. 

flanholes.  These  should  be  placed  at  all  changes  of  grade 
and  at  all  junctions  between  streets.  They  are  built  of  brick  and 
afford  access  to  the  sewer  for  inspection ;  in  addition  to  this  they 
are  sometimes  used  for  flushing.  They  are  provided  with  iron 
covers  which  are  often  pierced  with  holes  for  ventilation. 

Sewer  Grades.  The  grades  of  sewers  should  be  sufficient 
where  possible,  to  give  them  a  self-clearing  velocity.  Practical 
experiments  show  that  sewers  of  the  usual  sections  will  remain 
clear  with  the  following  minimum  grades:  Separate  house  con- 
nections, 2  per  cent;  (2-feet  fall  in  each  100  feet  of  length) 
small  street  sewers,  1  per  cent ;  main  sewers,  0.7  per  cent.  These 
grades  may  be  reduced  slightly  for  sewers  carrying  only  rain  or 
quite  pure  water. 

The  following  formula  may  be  used  for  computing  the  mini- 
mum grade  for  a  sewer  of  clear  diameter  equal  to  "d"  inches 
and  either  circular  or  oval  in  section. 

•     Minimum  grade,  in  per  cent  =      ,  ,  „    . 
5  «  +  5  0 

Flushing  Devices.     Where  very  low  grades  are  unavoidable 


459 


52  PLUMBING. 


and  at  the  head  of  branch  sewers,  where  the  volume  of  flow  is 
small,  flushing  may  be  used  with  advantage. 

In  some  cases  water  is  turned  into  the  sewer  through  a  man- 
hole, from  some  pond  or  stream,  or  from  the  public  water-works 
system.  Generally,  however,  the  water  is  allowed  to  accumulate 
before  being  discharged,  by  closing  up  the  lower  side  of  the  man- 
hole until  the  water  partially  fills  it,  then  suddenly  releasing  it 
and  allowing  the  water  to  rush  through  the  pipe.  Instead  of 
using  clear  water  from  outside  for  this  purpose,  it  may  be  sufficient 
at  some  points  on  the  system  to  simply  back  up  the  sewage,  by 
closing  the  manhole  outlet,  thus  flushing  the  sewer  with  the  sewage 
itself.  Where  frequent  and  regular  flushing  is  required,  automatic 
devices  are  often  used.  These  usually  operate  by  means  of  a  self- 
discharging  siphon,  although  there  are  other  devices  operated  by 
means  of  the  weight  of  a  tank  which  fills  and  empties  itself  at 
regular  intervals. 

House  Connections.  Provision  for  house  connections  should 
be  made  when  the  sewers  are  laid,  in  order  to  avoid  breaking  up 
the  streets  after  the  sewers  are  in  use.  Y  branches  should  be  put 
in  at  frequent  intervals,  say  from  25  feet  apart  upwards,  according 
to  the  character  of  the  street.  When  the  sewer  main  is  deep 
down,  quarter  bends  are  sometimes  provided,  and  the  house  con- 
nection pipe  carried  vertically  upwards  to  within  a  few  feet  of  the 
surface  to  avoid  deep  digging  when  connections  are  made.  Where 
house  connections  are  made  with  the  main,  or  where  two  sewers 
join,  the  direction  of  flow  should  be  as  nearly  in  the  same  direc- 
tion as  possible,  and  the  entering  sewer  should  be  at  a  little  higher 
level  in  order  to  increase  the  velocity  of  the  inflowing  sewage. 

Depth  of  Sewers  Below  the  Surface.  No  general  rule  can 
be  followed  in  this  matter  except  to  place  them  low  enough  to 
secure  a  proper  grade  for  the  house  connections,  which  are  to  be 
made  with  them.  They  must  be  kept  below  a  point  where  there 
would  be  trouble  from  freezing,  but  the  natural  depth  is  usually 
sufficient  to  prevent  this  in  most  cases. 

Ventilation  of  Sewers.  There  is  more  or  less  difference  in 
opinion  in  regard  to  the  proper  method  of  ventilating  sewer  mains. 
Ventilation  through  house  soil  pipes  is  generally  approved  where 
the  sewers  and  house  connections  are  properly  constructed  and 


460 


PLUMBING.  53 


operated,  and  where  the  houses  on  a  given  street  are  of  a  uniform 
height,  so  that  the  tops  of  all  the  soil  pipes  will  be  above  the  high- 
est windows.  Where  the  houses  are  uneven  in  height,  or  where 
the  sewerage  system  or  connections  are  not  well  designed  or  con- 
structed, it  is  recommended  that  main  traps  should  be  placed  on 
all  soil  pipes,  and  that  air  inlets  and  air  outlets  be  placed  on  the 
sewers  at  intervals  of  from  300  to  400  feet. 

The  Combined  System.  The  principal  differences  between 
this  and  the  separate  system  are  in  the  greater  size  of  conduits 
and  the  use  of  catch-basins  or  inlets  for  the  admission  of  surface 
water.  They  are  generally  of  brick,  stone  or  concrete,  or  a 
combination  of  these  materials,  instead  of  vitrified  pipe. 

Another  difference  is  the  provision  for  storm  overflows,  by 
means  of  which  the  main  sewers  when  overcharged  in  times  of 
heavy  rainfall  may  empty  a  part  of  their  contents  into  a  nearby 
stream.  At  such  times  the  sewage  is  diluted  by  the  rain-water, 
while  the  stream  which  receives  the  overflow  is  also  of  unusually 
large  size. 

Size,  Shape  and  Material.  The  actual  size  of  the  sewer, 
and  also  to  a  large  extent  its  shape  and  the  material  of  which  it  is 
constructed,  depends  upon  local  conditions.  Where  the  depth  of 
flow  varies  greatly  it  is  desirable  to  give  the  sewer  a  cross-section 
designed  to  suit  all  flows  as  fully  as  possible. 

The  best  form  to  meet  these  requirements  is  that  of  an  egg 
with  its  smaller  end  placed  downward.  With  this  form  the 
greatest  depth  and  velocity  of  flow  is  secured  for  the  smallest 
amount  of  sewage,  thus  reducing  the  tendency  to  deposits  and  stop- 
pages. Where  sewers  have  a  flow  more"  nearly  constant  and  equal 
to  their  full  capacity  the  form  may  be  changed  more  nearly  to  that 
of  an  ellipse.  F*or  the  larger  sewers  brick  is  the  most  common- 
material,  both  because  of  its  low  cost  and  the  ease  with  which  any 
form  of  conduit  is  constructed.  Stone  is  sometimes  used  on  steep 
grades,  especially  where  there  is  much  sand  in  suspension,  which 
would  tend  to  wear  away  the  brick  walls.  Concrete  is  used  where 
leakage  may  be  expected  or  where  the  material  is  liable  to  movement, 
but  is  more  commonly  used  as  a  foundation  for  brick  construction. 

A  catch-basin  is  generally  placed  at  each  street  corner  and 
provided  with  a  grated  opening  for  giving  the  surface  water  access 


461 


54  PLUMBING. 


to  a  chamber  or  basin  beneath  the  sidewalk,  from  which  a  pipe 
leads  to  the  sewer.  Catch-basins  may  be  provided  with  water 
traps  to  prevent  the  sewer  air  from  reaching  the  street,  but  traps 
fire  uncertain  in  their  action,  as  they  are  likely  to  become  unsealed 
through  evaporation  in  dry  weather.  To  prevent  the  carrying  of 
sand  and  dirt  into  the  sewers,  catch-basins  should  be  provided 
with  silt  chambers  of  considerable  depth,  with  overflow  pipes 
leading  to  the  sewer.  The  heavy  matter  which  falls  to  the 
bottoms  of  these  chambers  may  be  removed  by  buckets  and  carted 
away  at  proper  intervals. 

Storm  Overflows.  The  main  point  to  be  considered  in  the 
construction  of  storm  overflows  is  to  ensure  a  discharge  into 
another  conduit  when  the  water  readies  a  certain  elevation  in  the 
main  sewer.  This  may  be  carried  out  in  different  ways,  depending 
upon  the  available  points  for  overflow. 

Pumping  Stations.  The  greater  part  of  the  sewerage 
systems  in  the  United  States  operate  wholly  by  gravity,  but  in 
some  cases  it  is  necessary  to  pump  a  part  or  the  whole  of  the 
sewage  of  a  city  to  a  higher  level.  The  lifts  required  are  usually 
low,  so  that  high-priced  machinery  is  not  required.  In  general 
the  sewage  should  be  screened  before  it  reaches  the  pumps. 

Where  pumping  is  necessary,  receiving  or  storage  chambers 
are  sometimes  used  to  equalize  the  work  required  of  the  pumps, 
thus  making  it  possible  to  shut  down  the  plant  at  night.  Such 
reservoirs  should  be  covered,  unless  in  very  isolated  localities. 
The  force  main  or  discharge  pipe  from  the  pumps  is  usually  short, 
and  is  generally  of  cast  iron  put  together  in  a  manner  similar  to 
that  used  for  water-supply  systems. 

Tidal  Chambers.  Where  sewage  is  discharged  into  tide 
water  it  is  often  necessary  to  provide  storage  or  tidal  chambers,  so 
that  the  sewage  may  be  discharged  only  at  ebb  tides.  These  are 
constructed  similar  to  other  reservoirs,  except  that  they  must 
have  ample  discharge  gates,  so  that  they  may  be  emptied  in  a 
short  time.  They  are  sometimes  made  to  work  automatically  by 
the  action  of  the  tide. 

SEWAGE  PURIFICATION. 

Before  taking  up  this  subject  in  detail  it  is  well  to  consider 
what  sewage  is,  from  a  chemical  standpoint. 


462 


PLUMBING.  55 


When  fresh,  it  appears  at  the  mouth  of  an  outlet  sewer 
as  a  milky-looking  liquid  with  some  large  particles  of  matter 
in  suspension,  such  as  orange  peels,  rags,  paper  and  various 
other  articles  not  easily  broken  up.  It  often  has  a  faint, 
musty  odor  and  in  general  appearance  is  similar  to  the  suds-water 
tfrom  a  family  laundry.  Nearly  all  of  the  sewage  is  simply  water, 
the  total  amount  of  solid  matter  not  being  more  than  2  parts  in 
1,000,  of  which  half  may  be  organic  matter.  It  is  this  1  part  in 
1,000  which  should  be  removed,  or  so  changed  in  character  as  to 
render  it  harmless. 

The  two  systems  of  purification  in  most  common  use  are 
"  chemical  precipitation  "  and  the  "  land  treatment."  Mechanical 
straining,  sedimentation  and  chemical  precipitation  are  largely 
removal  processes,  while  land  treatment  by  the  slow  process  of 
infiltration,  or  irrigation,  changes  the  decaying  organic  matter  into 
stable  mineral  compounds. 

Sedimentation.  This  is  effected  by  allowing  the  suspended 
matter  to  settle  in  tanks.  The  partially  clarified  liquid  is  then 
drawn  off  leaving  the  solid  matter,  called  "  sludge"  at  the  bottom 
for  later  disposal.  This  system  requires  a  good  deal  of  time  and 
large  settling  tanks ;  therefore  it  is  suitable  only  for  small  quanti- 
ties of  sewage. 

Mechanical  Straining.  This  is  accomplished  in  different 
ways  with  varying  degrees  of  success.  Wire  screens  or  filters  of 
various  materials  may  be  employed.  Straining  of  itself  is  of  little 
value  except  as  a  step  to  further  purification.  Beds  of  coke  from 
6  to  8  inches  in  depth  are  often  used  with  good  results. 

Chemical  Precipitation.  Sedimentation  alone  removes  only 
such  suspended  matter  as  will  sink  by  its  own  weight  during  the 
comparatively  short  time  which  can  be  allowed  for  the  process. 

By  adding  certain  substances  chemical  action  is  set  up,  which 
greatly  increases  the  rapidity  with  which  precipitation  takes  place. 

Some  of  the  organic  substances  are  brought  together  by  the 
formation  of  new  compounds,  and  as  they  fall  in  flaky  masses 
they  carry  with  them  other  suspended  matter. 

A  great  number  and  variety  of  chemicals  have  been  employed 
for  this  purpose,  but  those  which  experience  has  shown  to  be  most 
useful  are  lime,  sulphate  of  alumina  and_some  of  the  salts  of  iron. 


463 


56  PLUMBING. 


The  best  chemical  to  use  in  any  given  case  depends  upon  the 
character  of  the  sewage  and  the  relative  cost  in  that  locality. 
Lime  is  cheap,  but  the  large  quantity  required  greatly  in- 
creases the  amount  of  sludge.  Sulphate  of  alumina  is  more 
expensive,  hut  is  often  used  to  advantage  in  connection  with 
lime.  Where  an  acid  sewage  is  to  be  treated,  lime  alone  should  be 
used. 

The  chemicals  should  be  added  to  the  sewage  and  thoroughly 
mixed  before  it  reaches  the  settling  tank  ;  this  mav  be  effected  by 
the  use  of  projections  or  baffling  plates  placed  in  the  condui'; 
leading  to  the  tank.  The  best  results  are  obtained  by  means  of 
long',  narrow  tanks,  and  they  should  be  operated  on  the  continue/us 
rather  than  the  intermittent  plan.  The  width  of  the  tank  should 
be  about  one-fourth  its  length.  In  the  continuous  method  the 
sewage  is  constantly  flowing  into  one  part  of  the  tank  and  dis- 
charging from  another.  In  the  intermittent  system  a  tank  is  lilled 
and  then  the  flow  is  turned  into  another,  allowing  the  sewage  in 
the  first  tank  to  come  to  rest.  In  the  continuous  plan  the  sewage 
generally  flows  through  a  set  of  tanks  without  interruption  until 
one  of  the  compartments  needs  cleaning.  The  clear  portion  is 
drawn  off  from  the  top,  the  sludge  is  then  removed,  and  the  tank 
thoroughly  disinfected  before  being  put  in  use  again.  The  satis- 
factory disposal  of  the  sludge  is  a  somewhat  difficult  matter.  The 
most  common  method  is  to  press  it  into  cakes,  which  greatly 
reduces  i.s  bulk  and  makes  it  more  easily  handled.  These  are 
sometimes  burned  but  are  more  often  used  for  fertilizing  purposes. 
In  some  cases  peat  or  other  absorbent  is  mixed  with  the  sludge 
and  the  whole  mass  removed  in  bulk.  In  other  instances  it  is  run 
out  on  the  surface  of  coarse  gravel  beds  and  reduced  by  draining 
and  drying.  In  wet  weather  little  drying  takes  place  and  during 
the  cold  months  the  sludge  accumulates  in  considerable  quantities. 
This  process  also  requires  considerable  manual  labor,  and  in  many 
cases  suitable  land  is  not  available  for  the  purpose.  The  required 
capacity  of  the  settling  tanks  is  the  principal  item  in  determining 
the  cost  of  installing  precipitation  works. 

In  the  treatment  of  house  sewage  provision  must  be  made  for 
about  TV  the  total  daily  flow,  and  in  addition  to  this,  allowance 
must  be  made  ^or  throwing  out  a  portion  of  the  tanks  for  cleaning 


464 


PLUMBING.  57 


and  repairs.  In  general,  the  tank  capacity  should  not  bo  much 
less  than  |  the  total  daily  flow. 

In  the  combined  system  it  is  impossible  to  provide  tanks  for 
the  total  amount,  and  the  excess  due  to  storm  water  must  dis- 
charge into. natural  water  courses  or  pass  by  the  works  without 
treatment. 

Broad  Irrigation  or  Sewage  Farming.  Where  sewage  is 
applied  to  the  surface  of  the  ground  upon  which  crops  are  raised 
the  process  is  called  "sewage  farming."  This  varies  but  little 
from  ordinary  irrigation  where  clean  water  is  used  instead  of 
sewage.  The  land  employed  for  this  purpose  should  have  a 
rather  light  and  porous  soil,  and  the  crops  should  be  such  as 
require  a  large  amount  of  moisture.  The  application  of  from 
5,000  to  10,000  gallons  of  sewage  per  day  per  acre  is  considered 
a  liberal  allowance.  On  the  basis  of  100  gallons  of  sewage  per 
head  of  population  this  would  mean  that  one  acre  would  care  for 
a  population  of  from  50  to  100  people. 

Sub-Surface  Irrigation.  This  system  is  employed  only 
upon  a  small  scale  and  chiefly  for  private  dwellings,  public  insti- 
tutions and  for  small  communities  where  for  any  reason  surface 
disposal  would  be  objectionable.  The  sewage  is  distributed 
through  agricultural  drain  tiles  laid  with  open  joints  and  placed 
only  a  few  inches  below  the  surface.  Provision  should  be  made 
for  changing  the  disposal  area  as  often  as  the  soil  may  require  by 
turning  the  sewage  into  sub-divisions  of  the  distributing  pipes. 

Intermittent  Filtration.  This  method  and  the  broad  irriga- 
tion already  described  arc  the  only  purification  processes  in  use  on 
a  large  scale  which  can  remove  practically  all  the  organic  matter 
from  sewage  without  being  supplemented  by  some  other  method. 
The  process  is  a  simple  one  and  consists  in  running  the  sewage 
out  through  distributing  pipes  onto  beds  of  sand  4  or  5  feet  in 
thickness  with  a  system  of  pipes  or  drains  below  for  collecting  the 
purified  liquid.  In  operation  the  sewage  is  first  turned  on  one 
bed  and  then  another,  thus  allowing  an  opportunity  for  the  liquid 
portion  to  filter  through.  As  the  surface  becomes  clogged  it  is 
raked  over  or  the  sludge  may  be  scraped  off  together  with  a  thin 
layer  of  sand.  The  best  filtering  material  consists  of  a  clean, 
sharp  sand  with  grains  of  uniform  size  such  that  the  free  space 


465 


58  PLUMBING. 


between  them  will  equal  about  one-third  the  total  volume.  When 
the  sewage  is  admitted  to  the  sand  only  a  part  of  the  air  is  driven 
out,  so  there  is  a  store  of  oxygen  left  upon  which  the  bacteria 
may  draw.  This  is  not  a  mere  process  of  straining  but  the  forma- 
tion of  new  compounds  by  the  action  of  the  oxygen  in  the  air, 
thus  changing  the  organic  matter  into  inorganic.  Much  depends 
upon  the  size  and  quality  of  the  sand  used.  The  grains  that  have 
been  found  to  give  the  best  results  range  from  .1  to  .5  of  an  inch 
in  diameter.  The  work  done  by  a  filter  is  largely  determined  by 
the  finer  particles  of  sand  and  that  used  should  be  of  fairly  uni- 
form quality,  and  the  coarser  and  finer  particles  should  be  well 
mixed.  The  area  and  volume  of  sand  or  gravel  required  are  so 
large -that  the  transportation  of  material  any  great  distance  cannot 
be  considered.  Usually  the  beds  are  constructed  on  natural 
deposits,  the  top  soil  or  loam  being  removed.  The  sewage  should 
be  brought  into  the  beds  so  as  to  disturb  their  surface  as  little  as 
possible,  and  should  be  distributed  evenly  over  the  whole  bed. 

The  under  drains  should  not  be  placed  more  than  50  feet 
apart,  usually  much  less,  and  should  be  provided  with  manholes 
at  the  junctions  of  the  pipes.  Before  admitting  the  sewage  to  the 
beds  it  is  usually  best  to  screen  it  sufficiently  to  take  out  paper, 
rags  and  other  lloating  matter.  The  size  of  each  bed  should  be 
such  as  to  permit  an  even  distribution  of  sewage  over  its  surface. 

Where  the  nitration  area  is  small,  it  must  be  divided  so  as  to 
permit  of  intermittent  operation  ;  that  is,  if  a  bed  is  to  be  in  use 
and  at  rest  for  equal  periods,  then  two  or  more  beds  would  be 
necessary,  the  number  depending  on  the  relative  periods  of  use 
and  rest.  Some  additional  area  should  also  be  piovided  for  emer- 
gency, or  for  use  while  the  beds  are  being  scraped.  If  a  large 
area  is  laid  out,  so  that  the  size  of  the  beds  is  limited  only  by 
convenience  in  use,  then  an  acre  may  be  taken  as  a  good  size. 

The  degree  .  of  purification  depends  upon  various  circum- 
stances, but  with  the  best  material  practically  all  of  the  organic 
matter  can  be  removed  from  sewage  by  intermittent  nitration  at  a 
rate  of  about  100,000  gallons  per  day. 

Theie  is  often  much  opposition  to  sewage  purification  by 
those  living  or  owning  property  near  the  plants  ;  but  experience 
has  shown  that  well-conducted  plants  are  inoffensive  both  within 


460 


PLUMBING.  59 


and  without  their  enclosures.  The  employees  about  such  worts 
are  as  healthy  as  similar  classes  of  men  in  other  occupations.  The 
crops  raised  on  sewage  farms  are  as  healthful  as  those  of  the  same 
kind  raised  elsewhere,  and  meat  and  milk  from  sewage  farms  are 
usually  as  good  as  when  produced  under  other  conditions.  Good 
design  and  construction,  followed  by  proper  methods  of  operation, 
are  all  that  are  needed  to  make  sewage  purification  a  success.  No 
one  system  can  be  said  to  be  the  best  for  all  localities.  The 
special  problems  of  each  case  must  be  met  and  solved  by  a  selec- 
tion from  among  the  several  systems  and  the  combinations  of 
systems,  and  parts  chosen  that  are  best  adapted  to  the  conditions 
at  hand. 


467 


PLUMBING. 

PART  II. 

DOHESTIC  WATER  SUPPLY. 

Hydraulics  of  Plumbing.  Although  the  principles  of  Hy- 
draulics and  Hydrostatics  are  discussed  in  "  Mechanics,"  it  will 
be  well  to  review  them  briefly,  showing  their  application  to  the 
various  problems  under  the  head  of  "  Water  Supply." 

If  several  open  vessels  containing  water  are  connected  by 
pipes,  the  water  will  eventually  stand  at  the  same  level  in  all  of 
them,  regardless  of  the  length  or  the  size  of  the  connecting  pipes. 

The  pressure  exerted  by  a  liquid  at  any  given  point  is  the 
same  in  all  directions,  and  is  proportional  to  the  depth. 

A  column  of  water  at  60°  temperature  having  a  sectional  area 
of  one  square  inch  and  a  height  of  one  foot,  weighs  .43  pound,  and 
the  pressure  exerted  by  a  liquid  is  usually  stated  in  pounds  per  square 
inch,  the  same  as  in  the  case  of  steam.  If  a  closed  vessel  is  con- 
nected, by  means  of  a  pipe,  with  an  open  vessel  at  a  higher  level, 
so  that  it  is  10  feet*  for  example,  from  the  bottom  of  the  first 
vessel  to  the  surface  of  the  water  in  the  second,  the  pressure  on 
each  square  inch  of  the  entire  bottom  of  the  lower  vessel  will  be 
10  X  .43  =  4.3  pounds,  and  the  pressure  per  square  inch  at  any 
given  point  in  the  vessel  or  connecting  pipe  will  be  equal  to  its 
distance  in  feet  from  the  surface  of  the  water  in  the  upper  vessel 
multiplied  by  .43.  If  a  pipe  is  carried  from  a  reservoir  situated 
on  the  top  of  a  hill  to  a  point  at  the  foot  of  the  hill  a  hundred  feet 
below  the  surface  of  the  water,  a  pressure  of  100  X  -43  —  43 
pounds  per  square  inch  will  be  exerted  at  the  lower  end  of  the 
pipe,  provided  it  is  closed.  When  the  pipe  is  opened  and  the 
water  begins  to  flow,  the  conditions  are  changed  and  the  pressure 
in  the  different  parts  of  the  pipe  varies  with  the  distance  from  the 
open  end. 

In  order  for  a  liquid  to  flow  through  a  pipe  there  must  be  a 
certain  pressure  or  "  head  "  at  the  inlet  end.  The  total  head  caus- 
ing the  flow  is  divided  into  three  parts,  as  follows:  1st,  the 


469 


PLUMBING. 


velocity  head :  the  height  through  which  a  body  must  fall  in  a 
vacuum  to  acquire  the  velocity  with  which  the  water  enters  the 
pipe.  2d,  the  entry  head :  that  required  to  overcome  the  resist- 
ance to  entrance  into  the  pipe.  3d,  the  friction  head:  due  to  the 
frictional  resistance  to  flow  within  the  pipe.  In  the  case  of  long 
pipes  and  low  heads  the  sum  of  the  velocity  and  entry  heads  is  so 
small  that  it  may  be  neglected. 

Table  I  shows  the  pressure  of  water  in  pounds  per  square 
inch  for  elevations  varying  in  height  from  1  to  185  feet. 

Table  II  gives  the  drop  in  pressure  due  to  friction  in  pipes  of 
different. diameters  for  varying  rates  of  flow.  The  figures  given 
are  for  pipes  100  feet  in  height.  The  frictional  resistance  in 
smooth  pipes  having  a  constant  flow  of  water  through  them  is  pro- 
portional to  the  length  of  pipe.  That  is,  if  the  friction  causes  a 
drop  in  pressure  of  4.07  pounds  per  square  inch  in  a  l|-incli  pipe 
100  feet  long,  which  is  discharging  20  gallons  per  minute,  it  will 
cause  a  drop  of  4.07  X  2  =  8. 14  pounds  in  a  pipe  200  feet  long;  or 
4.07  -f-  2  =  2.03  pounds  in  a  pipe  50  feet  long,  acting  under  the 
same  conditions.  The  factors  given  in  the  table  are  for  pipes  of 
smooth  interior,  like  lead,  brass  or  wrought  iron. 

Example. —  A  1-i-inch  pipe  100  feet  long  connected  with  a 
cistern  is  to  discharge  35  gallons  per  minute.  At  what  elevation 
above  the  end  of  the  pipe  must  the  surface  of  the  water  in  the 
cistern  be  to  produce  this  flow? 

In  Table  II  we  find  the  friction  loss  for  a  1  i-inch  pipe  dis- 
charging 35  gallons  per  minute  to  be  5.05  pounds.  In  Table  I  we 
find  a  pressure  of  5.2  pounds  corresponds  to  a  head  of  12  feet, 
which  is  approximately  the  elevation  required. 

How  many  gallons  will  be  discharged  through  a  2-inch  pipe 
100  feet  long  where  the  inlet  is  22  feet  above  the  outlet?  In 
Table  I  wo  find  a  head  of  22  feet  corresponds  to  a  pressure  of  9.53 
pounds.  Then  looking  in  Table  IT  we  find  in  the  column  of  Fric- 
tion Loss  for  a  2-inch  pipe  that  a  pressure  of  9.46  corresponds  to 
a  discharge  of  100  gallons  per  minute. 

Tables  I  and  II  are  commonly  used  together  in  examples. 

A  house  requiring  a  maximum  of  10  gallons  of  water  pel 
minute  is  to  be  supplied  from  a  sp'/ing  which  is  located  600  feet 
distant,  and  at  an  elevation  of  50  feet  above  the  point  of  dis- 


470 


PLUMBING. 


TABLE 


Head 
in 
feet. 

Pressure 
pounds  per 
square  inch. 

Head 
in 
feet. 

Pressure 
pounds  per 
square  inch. 

Head 
in 

feet. 

Pressure 
pounds  per 
square  inch. 

1 

.43 

46 

19.92 

91 

39.42 

2 

.86 

47 

20.35 

92 

•    39.85 

3 

1.30 

48 

20.79 

93 

40.28 

4 

1.73 

49 

21.22 

94 

40.72 

5 

2.16 

50 

21.65 

95 

41.15 

6 

2.59 

51 

22.09 

96 

41.58 

7 

3.03 

52 

22.52 

97 

42.01 

'8 

3.46 

53 

22.95 

98 

42.45 

9 

3.89 

54 

23.39 

99 

42.88 

10 

433 

55 

23.82 

100 

43.31 

11 

4.76 

56 

24.26 

101 

43.75 

12 

5.20 

57 

24.69 

102 

44.18 

13 

5.63 

58 

25.12 

103 

44.61 

14 

6.06 

59 

25.55 

104 

45.05 

15 

6.49 

60 

25.99 

105 

45.48 

16 

6.92 

61 

26.42 

106 

45.91 

17 

7.36 

62 

26.85 

107 

46.34 

18 

7.79 

63 

27.29 

108 

46.78 

19 

8.22 

64 

27.72 

109 

47.21 

20 

8.66 

65 

28.15 

110 

47.64 

21 

9.09 

66 

28;58 

111 

48.08 

22 

9.53 

67 

29.02 

112 

48.51 

23 

9.96 

68 

29.45 

113 

48.94 

24 

10.39 

69 

29.88 

114 

49.38 

25 

10.82 

70 

30.32 

115 

49.81 

26 

11.26 

71 

30.75 

116 

50.24 

27 

11.69 

72 

31.18 

117 

50.68 

28 

1.2.12 

73 

31.62 

118 

51.11 

29 

12.55 

74 

32.05 

119 

51.54 

30 

12.99 

75 

32.48 

120 

51.98 

31 

13.42 

76 

32.92 

121 

52.41 

32 

13.86 

77 

33.35 

122 

52.84 

33 

14.29 

78 

33.78 

123 

53.28 

34 

14.72 

79 

34.21 

124 

53.71 

35 

15.16 

80 

34.65 

125 

54.15 

36 

1  5.59 

81 

35.08 

126 

54.58 

37 

16.02 

82 

35.52 

127 

55.01 

38 

16.45 

83 

35.95 

128 

55.44 

39 

16.89 

84 

36.39 

129 

55.88 

40 

17.32 

85 

36.82 

130 

56.31 

4.1 

17.75 

86 

37.25 

131 

56.74 

42 

18.19 

87 

37.68 

132 

57.18 

43 

18.62 

88 

38.12 

133 

57.61 

44 

19.05 

89 

38.55 

134 

58.04 

45 

19.49 

90 

38.98 

135 

58.48 

471 


PLUMBING. 


charge.  What  size  of  pipe  will  be  required?  From  Table  I  we 
find  an  elevation  or  head  of.  50  feet  will  produce  a  pressure  of  21.65 
'pounds  per  square  inch.  Then  if  the  length  of  the  pipe  were 
only  100  feet,  we  should  have  a  pressure  of  21.65  pounds  avail- 
able to  overcome  the  friction  in  the  pipe,  and  could  follow  along  the 
line  corresponding  to  10  gallons  in  Table  II  until  we  came  to  the 

TABLE  II. 


J 

n. 

i 

m. 

1 

in. 

11 

in. 

11 

in. 

2 

in. 

2J 

in. 

3 

n. 

rged  per 

ft 

1 

h 
P. 

1 

1 

1 

Pi 
| 

! 

a 

~ 
| 

•H 

| 

I 

a 

OQ 

o 

a 

1 

c 

£ 
o 

a 

I 

HH 

a 

I 

>, 

a  • 

>, 

s   • 

>> 

fl   • 

^ 

a   • 

>J 

a  • 

X 

a 

K^ 

§1 

35 

C  5 

11 

0  a 

p>   02 

•II 
It 

Velocit 
second 

.2-c 

*i  a 

ll 

.tJ-c 

og 

>8 

.2-0 
"5  ° 

Si 

Velocit 
second 

Frictio 
pounds 

Velocit 
second 

Frictio 
pounds 

Velocit 
second 

Frictio 
pounds 

Velocit 
second 

.2-a 

°  3 

£  P. 

11 

0)   " 

>•  cfl 

Frictio 
pounds 

5 

8.17 

24.6 

3.63 

33 

2.04 

.84 

1.31 

.31 

.91 

.12 

in 

163 

96.0 

7.25 

13.0 

4.08 

3.16 

2.61 

1.05 

1.82 

.47 

1.02 

.12 

IS 

10.9 

6.13 

6.98 

3.92 

2.38 

2.73 

.97 

1.53 

.27 

20 

14.5 

50.4 

8.17 

12.3 

5.22 

4.07 

3.63 

1.66 

2.04 

42 

25 

18.1 

78.0 

10.2 

19.0 

6.53 

6.40 

4.54 

2.62 

2.55 

.67 

1.63 

.21 

1.13 

.10 

an 

12.3 

27.5 

7.84 

9.15 

5.45 

3.75 

3.06 

.91 

35 

14.3 

370 

9.14 

1204 

6  36 

5.05 

3.57 

1.25 

111 

16.3 

48.0 

10.4, 

16.10 

7.26 

6.52 

4.09 

1.60 

4ft 

11.7 

20.2 

8.17 

8.15 

4.60 

2.02 

•",!  I 

13.1 

24.9 

9.08 

10.0 

5.11 

244 

326 

.81 

2.27 

85 

75 

19.6 

56.1 

13.6 

22.4 

7.66 

5.32 

4.90 

1.80 

3.40 

.74 

[00 

18.2 

39.0 

10.2 

9.46 

6.53 

3.20 

4.54 

1.31 

1  "l 

12.8 

14.9 

8.16 

4.89 

5.67 

1  99 

1  M  1 

15.3 

21.2 

980 

7.00 

6.81 

285 

175 

17.1 

28.1 

11.4 

9.46 

7.94 

3>5 

200 

20.4 

37.5 

13.1 

12.47 

9.08 

5.02 

friction  loss  corresponding  most  nearly  to  21.65,  and  take  the  size  of 
pipe  corresponding.  But  as  the  length  of  the  pipe  is  600  feet,  the 
friction  loss  will  be  six  times  that  given  in  Table  II  for  given  sizes 
of  pipe  and  rates  of  flow ;  hence  we  must  divide  21.65  by  6  to  ob- 
tain the  available  head  to  overcome  friction,  and  look  for  this 
quantity  in  the  table,  21.65  -^-  6  —  3.61,  and  Table  II  shows  i.s 
that  a  1-inch  pipe  will  discharge  10  gallons  per  minute  with  a 
friction  loss  of  3.16  pounds,  and  this  is  the  size  we  should  use. 

EXAHPLES  FOR  PRACTICE. 

1.     What  size  pipe  will  be  required  to  discharge  40  gallons 
per  minute,  a  distance  of  50  feet,  with  a  pressure  head  of  19  feet? 

Ans.   1|  inch. 


472 


PLUMBING. 


2.  What  head  will  be  required  to  discharge  100  gallons  per 
minute  through  a  2* -inch  pipe  700  feet  long? 

Ans.  52  feet. 
PIPING. 

Wrought  iron,  lead  and  brass  are  the  principal  materials 
used  for  water  pipes.  Wrought-iron  pipe  is  the  cheapest  and 
easiest  to  lay,  but  is  objectionable  on  account  of  rust  and  the 
consequent  discoloration  of  water  passing  through  it.  When  it 

TABLE  III. 


| 

•3 

1 

5 

Q> 

, 

S 

per  square 
urface. 

per  square 
surface. 

H 

"3 
1 

1 

a 

a 

"5  . 

« 

5 

n 

il  outside  c 

I 

il  inside  di 

•nal  circum 

,h  of  pipe 
of  inside  - 

,h  of  pipe 
,  of  outside 

oj 

13 
a 

\ 

"3 
a 

h  of  pipe< 
bic  foot. 

ht  per  foot. 

1 
?! 

13 

t 

> 

I 

5 

ns  per  foot 

I 

1 

5 

1 

1 

i 

|l 

r 

1 

H 

1! 

tt 
1 

I 

! 
i 

O 

in. 

in. 

in. 

in. 

in. 

in. 

feet 

feet 

in. 

in. 

feet 

pounds 

. 

.40 

.068 

.27 

.85 

1.27 

14.1 

9.44 

.05 

.13 

2500. 

.24 

27 
18 

.0006 
.0026 

'I 

.54 

.088 

.36 

1.14 

1.69 

10.5 

7.05 

.10 

.23 

1385. 

.42 

U 

.0057 

. 

.67 

.091 

.49 

1.55 

2.12 

7.67 

5.65 

.19 

.36 

751.5 

.56 

1  1 

.0102 

: 

.84 

.109 

.62 

1.95 

2.65 

8.13 

4.50 

.30 

.55 

472.4 

.84 

14 

.0230 

• 

1.05 

.113 

.82 

259 

3.29 

4.63 

3.63 

.53 

.86 

270.0 

1.12 

ll 

.0408 

1 

1.31 

.134 

1.05 

3.29 

4.13 

3.68 

2.90 

.86 

1.35 

166.9 

1.67 

ll 

.0638 

166 

.140 

1.38 

4.33 

5.21 

2.77 

2.30 

1.49 

2.16 

96.2 

2.26 

11 

.0918 

ij 

1.90 

.145 

1.61 

5.06 

5.96 

2.37 

2.01 

2.04 

2.83 

70.6 

2.69 

11 

.1632 

X 

2.37 
287 

.154 
.204 

2.06 
247 

6.49 
7.75 

7.46 
9.03 

1.85 
1.54 

1.61 
1  33 

3.35 

4.78 

4.43 
6.49 

42.3 
30  1 

3.66 
5.77 

8 
8 

.2550 
.3673 

:i 

3.50 

.217 

3.06 

9.63 

10.1 

1.24 

1.09 

7.39 

9.62 

19.5 

7.54 

8 

.4998 

3J 

4.00 

.226 

3.55 

11.1 

12.5 

1.07 

.95 

988 

12.5 

14.5 

9.05 

H 

.6528 

f 

4.50 

.237 

402 

12.6 

14.1 

.95 

.85 

12.7 

15.9 

11.3 

10.7 

X 

.8263 

6 

6 

5.56 
6.62 

.259 
.280 

5.04 
6.06 

15.8 
19.0 

17.4 
20.8 

.75 

.63 

.57 

20.0 
28.9 

24.3 
34.4 

7.2 
4.9 

IS 

8 
'8 

1.469 
1.999 

is  employed  for  this  purpose  it  is  customary  to  use  galvanized 
pipe,  that  is,  pipe  which  has  been  covered  with  a  thin  coating  of 
zinc  or  zinc  and  tin.  This  prevents  rust  from  forming  where  the 
zinc  is  unbroken,  but  at  the  joints  where  threads  are  cut,  and  at 
other  places  where  the  zinc  becomes  loosened,  as  by  bending,  the 
pipe  is  likely  to  be  eaten  away  more  or  less  rapidly,  depending 
upon  the  quality  of  the  water.  Zinc,  when  taken  into  the 
system,  is  poisonous,  and  for  this  reason  galvanized  pipes  should 
not  ordinarily  be  used  for  drinking  water. 


473 


8 


PLUMBING. 


Table  III  gives  the  various  dimensions  of  wrought-iron  pipe. 
In  using  pipe  of  this  kind,  it  is  well  to  allow  something  in  size 
for  possible  choking  by  rust  or  sediment.  While  galvanized 
pipe  does  not  rust,  for  a  time  at  least,  there  is  likely  to  be 
a  roughness  which  causes  an  accumulation  of  more  or  less 
sediment. 

TABLE  IV. 

Lead  Pipe. 


if 

s 

1 

p.  5 

"S 

"Q 

be  ?- 

g 

1 

•2 

s  °° 

2 

"3 

.2 
•3 

I 

£ 
a 

1  I 

1 

a 
55 

a 

ft 

&o 

•°    r§ 
§5 

a 

1 

2 

g 

1 

3 

.75 

.18 

1  Ib.  12  oz. 

1968 

492 

3 

.55 

.087 

10 

1085 

271 

i 

1.00 

.25 

3 

1787 

446 

* 

.63 

.065 

10 

625 

156 

| 

1.10 

.23 

3    8 

1548 

387 

f  ' 

.84 

.10 

1    4 

708 

177 

1.33 

.29 

4   14 

1462 

365 

1 

.93 

.09 

1    3 

505 

126 

1 

1.60 

.30 

6 

1230 

307 

1 

1.18 

.09 

1    8 

325 

81 

H 

1.80 

.275 

6   12 

962 

240 

H 

1.44 

.095 

2 

322 

80 

H 

2.08 

.29 

8 

742 

185 

1.74 

.12 

3 

245 

61 

if 

2.12 

.19 

5 

460 

116 

if 

2.0 

.125 

3   10 

318 

79 

2 

2.60 

.30 

10   11 

611 

152 

2 

2.18 

.09 

4 

200 

50 

Iron  pipe  having  a  lining  of  tin  Jg  inch  or  more  in  thickness 
is  now  manufactured,  but  being  a  comparatively  new  product,  its 
wearing  qualities  have  not  yet  been  thoroughly  tested. 

Lead  Pipe  is  the  best  and  most  widely  used  for  domestic 
water  supply.  Although  poisonous  under  certain  conditions,  as 


474 


§s 

S5    >> 

2* 
w« 
S^ 

I! 


PLUMBING. 


when  new  and  bright  and  when  used  with  very  pure  water,  it 
usually  becomes  coated  with  a  scale  which  makes  it  practically 
Harmless.  It  is  more  costly  than  iron  pipe,  and  requires  more 
skill  in  laying  and  making  up  the  joints.  It  is  less  likely  to  burst 
from  the  action  of  frost,  as  it  is  a  soft  metal  and  stretches 
with  the  expansion  of  the  ice  in  the  pipe.  When  it  does 
break  under  pressure  it  generally  occurs  in  small  holes  not 
over  an  inch  long,  which  are  easily  repaired  without  removing 
any  part  of  the  pipe,  while  in  the  case  of  iron  pipe  the  cracks 
generally  extend  the  entire  length  of  the  section  in  which  the 

TABLE  V. 

Tin-lined  Lead  Pipe. 


1 

I 

1 

1 

1 

| 

| 

j 

| 

1 

•3 
"3 

2jf 

Sf 

«* 

„! 

ojf 

«$ 

|I 

•$ 

|! 

a 

A 

A 

A 

43 

i 

i 

I 

<o 

'3 

<a 

a) 

«" 

w 

•3 

lb.    oz. 

lb.    oz. 

lb.    oz. 

lb.    oz. 

lb.    oz. 

lb.    oz. 

lb.  oz. 

lb.    oz. 

Ib.oz. 

1      8 

i    5 

1      2 

1      0 

0    13 

10 

0      8 

i 

3      0 

2      0 

12 

1      4 

1      0 

13 

0    11 

0      9 

6 

3      8 

2    12 

8 

2      0 

1    12 

8 

1    4 

1      0 

0    12 

1 

4      8 

3      8 

\       0 

2      4 

2      0 

12 

1    8 

1      4 

1      0 

1 

6      0 

4    12 

'        0 

3      4 

2      8 

0 

1      8 

6    12 

5    12 

12 

3    12 

3      0 

8 

2      0 

M 

9      0 

8      0 

4 

5      0 

4      4 

8 

3      4 

9      0 

water  is  frozen,  and  new  pipe  will  be  required.  Lead  pipe 
is  commonly  made  in  six  different  thicknesses  or  weights,  desig- 
nated as  AAA,  AA,  A,  B,  C  and  D,  in  which  AAA  is  the 
heaviest  and  D  the  lightest.  Table  IV  gives  the  principal  prop- 
erties of  the  heaviest  and  lightest  weight  for  lead  pipe  of  different 
diameters. 

Tin-lined  lead  pipe  is  used  to  some  extent  for  conveying 
water  for  domestic  purposes.  The  principal  objection  to  this  pipe 
lies  in  the  difficulty  experienced  in  making  the  joints.  Tin  melts 
at  a  considerably  lower  temperature  than  lead,  so  that  in  making 
wipe  joints  it  is  likely  to  melt  before  the  lead  and  block  up  the 
passage  through  the  pipe.  Another  objection  is  due  to  the  fact 


475 


10 


PLUMBING. 


that  the  tin  lining  and  the  outer  lead  covering  are  simply  pressed 
together,  and  it  often  happens  that  in  bending  the  pipe  the  lining 
pulls  away  from  the  lead,  thus  both  obstructing  and  weakening 
the  pipe.  When  used  for  hot  water,  the  uneven  expansion  of  the 
two  metals  may  separate  the  two  layers,  and  so  cause  the  same 
difficulties  already  mentioned. 

Table  V  gives  some  of  the  properties  of  tin-lined  lead  pipe. 


WAT£R    LEVEL 
/N    WCLL 


Fig.  2. 


The  strength  of  tin-lined  pipe  is  about  the  same  as  that  of  lead 
pipe,  the  greater  strength  of  the  tin  being  offset  by  the  lighter 
weight  of  the  pipe  made  in  this  way. 

Brass  Pipe.  Brass  is  one  of  the  best  materials  for  hot- 
water  pipes,  and  should  be  used  where  the  cost  is  not  the  control- 
ling feature.  It  is  commonly  employed  for  connecting  pumps  and 
boilers  and  for  the  steam-heating  coils  inside  laundry-water 
heaters.  It  is  often  used  for  the  connections  between  the  kitchen 
hot-water  tank  and  range,  and  when  nickel  plated  is  extensively 
employed  in  connection  with  bathroom  fixtures.  The  sizes  and 
thicknesses  are  approximately  the  same  as  wrought-iron  pipe. 


47G 


PLUMBING.  11 


PUHPS. 

The  principle  upon,  which  the  pump  operates  has  already 
been  taken  up  in  the  Instruction  Paper,  "  Mechanics."  The 
more  common  forms  are  known  as  the  "lift  pump,"  the  "suction 
pump"  and  a  combination  of  the  two  called  the  "deep  well 
pump." 

Fig.  1  shows  a  pump  of  the  first  kind.  In  this  pump  A  is 
the  cylinder,  B  the  plunger,  C  the  bottom  valve  and  D  the 
plunger  valve.  When  the  plunger  is  drawn  up,  a  vacuum  is 
formed  in  the  cylinder,  and  water  flows  in  through  C  to  fill  it. 
When  the  plunger  is  forced  down,  valve  D  opens  and  allows  the 
water  to  flow  through  the  plunger  while  C  remains  closed.  As 
this  operation  is  repeated,  the  water  is  raised  by  the  plunger  at 
each  stroke  until  the  entire  length  of  the  pump  barrel  is  filled, 
and  it  will  then  flow  from  the  spout  in  an  intermittent  stream. 

In  the  suction  pump  shown  in  Fig.  2,  the  cylinder  and  valves 
are  the  same,  but  they  are  placed  at  the  top  of  the  well  and  are 
connected  with  the  water  below  by  means  of  a  pipe,  as  shown. 
When  the  pump  is  operated,  a  vacuum  is  formed  in  the  cylinder 
and'pipe  below  the  plunger,  and  the  pressure  of  the  atmosphere 
upon  the  surface  of  the  water  forces  it  up  the  pipe  and  fills  the? 
chamber,  after  which  the  action  becomes  the  same  as  in  the  case 
of  a  lift  pump.  The  pressure  of  the  atmosphere  is  approximately 
15  pounds  per  square  inch,  which  corresponds  to  the  weight  of  a 
column  of  water  34  feet  high,  which  is  the  height  that  the  water 
may  be  raised  theoretically  by  suction. 

When  the  surface  of  the  water  is  a  greater  distance  than  this 
below  the  point  of  discharge,  a  pump  similar  to  that  shown  in  Fig. 
3  must  be  used.  A  is  a  cylinder  with  plunger  and  valves  similar 
to  those  of  a  suction  pump.  The  cylinder  is  supported  in  the  well 
at  some  point  less  than  34  feet  above  the  surface  of  the  water ;  E 
is  an  air  chamber  connecting  with  the  upper  part  of  the  pump 
cylinder,  and  F  a  discharge  pipe  leading  from  the  bottom  of  the 
air  chamber  E.  The  action  is  as  follows :  water  is  pumped  into 
the  bottom  of  the  air  chamber,  and  as  it  rises  and  seals  the  end 
of  the  discharge  pipe,  the  air  in  the  upper  part  of  the  chamber 
is  compressed,  and  as  soon  as  sufficient  pressure  is  obtained  the 
water  is  forced  out  through  the  discharge  pipe  F.  The  pressure 


477 


12 


PLUMBING. 


required  in  the  air  chamber  depends  upon  the  height  to  which  the 

water  is  raised. 

The    Hydraulic    Ram.      This   is   a    device    for    automatically 

raising  water  from  a  lower  to  a  higher  level,  the  only  requirements 

within  certain  limits  being  that 
the  ram  shall  be  placed  at  a  given 
distance  from  the  spring  or  source 
of  supply  and  at  a  lower  level, 
depending  upon  the  height  to 
which  the  water  is  to  be  raised 
and  the  length  of  the  pipe  through 
which  it  is  to  be  forced.  The 
distance  from  the  source  or 
spring  to  the  ram  should  be  at 
least  from  25  to  50  feet,  in  order 
to  secure  the  required  velocity 
for  proper  operation.  A  differ- 
ence in  level  of  2  feet,  or  even 
less,  is  sufficient  to  operate  the 
ram  ;  but  the  greater  the  differ- 
ence, the  more  powerful  is  its 
operation.  For  ordinary  pur- 
poses, where  the  water  is  to  be 
conveyed  from  50  to  60  rods, 
about  -J0-  to  -^  of  the  total  amount 


used  can  be  raised  and  dis- 
charged at  an  elevation  ten 
times  as  great  as  the  fall  from 
the  spring  to  the  ram. 

In    Fig.    4,    A    represents 


Fig.  3. 


the  source  or  spring,  B  the  supply  pipe,  C  a  valve  opening  up- 
ward, D  an  air  chamber,  E  a  valve  closing  when  raised,  and  F 
the  discharge  pipe.  When  the  water  in  the  pipe  is  at  rest, 
the  valve  E  drops  by  its  own  weight  and  allows  the  water 
to  flow  through  it.  As  soon  as  a  sufficient  velocity  is  reached 
by  the  water,  its  momentum  or  force  raises  the  valve  against  its 
seat  and  closes  it.  The  water  being  thus  suddenly  arrested  in  its 


478 


PLUMBING. 


13 


passage  flows  into  the  chamber  D,  where  its  sudden  influx  com- 
presses the  air  in  the  top  of  the  chamber,  and  this  in  turn  forces 
the  water  upward  through  the  discharge  pipe  F.  As  soon  as  the 
water  in  the  pipe  B  becomes  quiet,  the  valve  E  again  opens  and 
the  operation  is  repeated.  Bends  in  either  the  drive  or  discharge 
pipe  should  be  avoided  if  possible.  If  elbows  are  necessary,  the 
extra  long  turn  pattern  should  be  used  in  order  to  give  as  little 
resistance  as  possible.  These  machines  are  made  of  iron  and 


TIC.  aoo' 
Fig.  5. 


Fig.  4. 

brass.  The  valve  and  stem  are  of 
bronze,  on  account  of  its  wear- 
ing qualities. 

Cisterns  and  Tanks.  Water 
cisterns  and  tanks  are  made  of 
various  materials  and  in  different 
shapes  and  sizes,  according  to 
the  special  uses  for  which  they  are  required.  A  durable  and 
satisfactory  tank  may  be  made  of  heavy  woodwork  or  plank 
bolted  together  with  iron  rods  and  nuts  and  then  lined  with  some 
sheet  metal,  such  as  copper,  lead  or  zinc.  Copper  or  lead  makes 
the  best  lining,  as  the  zinc  has  a  greater  tendency  to  corrode  and 
become  leaky.  If  copper  is  used,  it  should  be  tinned  on  the  out- 
side. Fig.  5  shows  a  wooden  tank  in  plan,  with  the  method  of 
locking  the  joints  in  the  copper  lining.  All  naib  should  be 
so  placed  as  to  be  covered  by  the  copper,  and  the  joints  soldered 
with  the  best  quality  of  .solder,  which  should  be  allowed  to 
into  the  seams.  If  the  tank  is  lined  with  lead,  a  good 


470 


1 1 


PLUMBING. 


should  be  used  (about  six  pounds  per  square  foot)  and  the  joints 
carefully  wiped  by  an  experienced  workman.  If  used  for  the 
storage  of  drinking  water,  this  form  of  lining  is  open  to  the  same 
objections  as  lead 'pipe,  but  if  kept  filled  at  all  times,  and  espe- 
cially if  the  water  contains  mineral  matter  to  any  extent,  there  is 
very  little  danger,  as  a  coating  is  soon  formed  over  the  surface  of 
the  lead,  protecting  it  from  the  action  of  the  water. 


Fig.  C. 

Cast-iron  sectional  tanks  can  be  had  in  almost  any  size  or 
shape.  A  tank  of  this  form  is  shown  in  Fig.  6.  It  is  made  up  of 
plates  which  are  planed  and  bolted  together,  the  joints  being  made 
tight  with  cement.  The  sections  are  made  in  convenient  sizes,  so 
that  they  may  be  handled  easily  and  conveyed  without  difficulty 
through  small  openings  to  any  part  of  the  house.  These  tanks 
are  easily  set  up,  and  are  practically  indestructible.  Wrought- 
iron  tanks  are  often  used,  but  are  not  as  easily  handled  as  either 
of  the  kinds  just  described.  Table  VI  will  be  found  useful  in 
computing  the  size  of  cylindrical  tanks. 

COLD-WATER  SUPPLY. 

Systems.  There  are  two  general  methods  of  supplying  a 
building  with  water,  one  known  as  the  "  direct  supply "  system, 
and  the  other  as  the  "indirect"  or  "tank"  system. 

In  the  direct  system  each  fixture  is  connected  with  the 
supply  pipe  and  is  under  the  same  pressure  as  the  street  main, 


480 


PLUMBING. 


16 


unless  a  reducing  valve  is  introduced.  This  system  is  not  always 
desirable,  as  the  street  pressure  in  many  places  is  likely  to  vary, 
especially  where  the  water  is  pumped  into  the  mains.  A  variable 
pressure  is  injurious  to  the  fixtures,  causing  them  to  leak  much 
sooner  than  if  subjected  to  a  steady  pressure.  Where  the  pres- 
sure in  the  street  main  exceeds  40  pounds  per  square  inch,  a 
reducing  valve  should  be  used  if  the  direct  system  is  to  be 
employed. 

TABLE  VI. 

Capacity  of  Cisterns,  in  Gallons,  for  each  10  inches  in  Depth. 


Diam- 
eter in 
feet. 

Gallons. 

Diam- 
eter in 
feet. 

Gallons. 

Diam- 
eter in 
feet. 

Gallons. 

2.0 

19.5 

6.0 

176.3 

10 

489.6 

2.5 

30.5 

6.5 

206.8 

11 

592.4 

3.0 

44.6 

7.0 

239.9 

12 

705.0 

3.5 

60.0 

7.5 

275.4 

13 

827.4 

4.0 

78.3 

8.0 

313.3 

14 

959.6 

4.5 

99.1 

8.5 

353.7 

15 

1101.6 

5.0 

122  A 

9.0 

396.5 

20 

1958.4 

5.5 

148.1 

9.5 

461.4 

25 

3059.4 

The  following  factors  for  changing  a  given  quantity  of  water 
from  one  denomination  to  another  will  often  be  found  useful  : 

Cubic  feet  X  62%  =  Pounds 
•  Pounds  -*-  62>£  =  Cubic  feet 
Gallons  X  8.3  =  Pounds 
Pounds  -^  8.3  =  Gallons 
Cubic  feet  X  7.48  =  Gallons 
Gallons  H-  7.48  =  Cubic  feet 

For  domestic  purposes  the  indirect  system  is  much  better. 
In  this  case  the  connection  with  the  street  main  is  carried  directly 
to  a  tank  placed  in  the  attic  or  at  some  point  above  the  high- 
est fixture,  and  all  the  water  used  in  the  house  discharged  into 
it.  The  supply  of  water  is  regulated  by  a  ball-cock  in  the 
tank  which  shuts  it  off  when  a  certain  level  is  reached.  All  the 
plumbing  fixtures  are  supplied  from  the  tank,  and  are  therefore 


481 


16 


PLUMBING. 


under  a  constant  pressure.  This  pressure  depends  upon  the  dis- 
tance of  the  fixture  below  the  tank.  The  pipes  and  fixtures  in  a 
house  supplied  with  the  tank  system  will  last  much  longer  and 


Jv 


TO  f?ANG£  BO/L£R 


J 


give  much  better  results  than  if  connected  directly  with  the  street 
main.  The  tank  is  also  found  useful  for  storage  purposes  in  case 
of  repairs  to  the  street  mains,  which  is  often  a  matter  of  much 
inconvenience. 

Fig.  7  sho\v  s  the  general  arrangement  of  the  cold-water  pipes 
of  an  indirect  supply  system.    On  the  right  is  shown  the  service 


482 


PLUMBING. 


17 


pipe,  which  is  carried  directly  from  the  street  to  the  attic,  and 
then  connected  with  a  ball-cock  located  inside  the  house  tank. 
A  supply  pipe  is  taken  from  the  bottom  of  the  tank  and  carried 
downward  through  the  building  for  supplying  the  various  fixtures. 
A  stopcock  should  be  placed  in  the  supply  pipe  for  closing  off 
the  tank  connections  in  case  of  repairs  to  the  house-piping  or 
fixtures. 

Tank  Overflow  Pipe.  In  order  to  prevent  any  possibility 
of  overflow,  every  house  tank  should  be  supplied  with  an  overflow 
pipe  of  sufficient  size  to  carry  off  easily  the  greatest  quantity  of 
water  that  may  be  discharged  into  it.  The  overflow  from  a  house 
tank  should  never  be  connected  directly  with  a  sewer  or  soil  pipe, 
even  if  provided  with  traps,  for  the  water  may  seldom  flow 


SERVICE 

OCK 

LEAD  STREET 

PIPE).    \      jf^.  MAIN 


Fig.  8. 

through  this  pipe,  thus  allowing  the  trap  to  become  unsealed 
through  evaporation.  It  is  much  better  to  let  the  end  of  the 
overflow  pipe  be  open  to  the  atmosphere  or  drop  over  some  fixture 
which  is  in  constant  use. 

Service  Pipe  Connections.  Fig.  8  shows  the  usual  method 
of  connecting  the  service  pipe  with  the  street  main.  The  service 
cock  is  connected  directly  with  the  main,  and  should  be  carefully 
blocked,  so  that  any  pressure  of  earth  from  above  will  not  break 
the  connection  or  strain  the  cock.  To  do  this  properly,  the  earth 
under  the  pipe  should  be  rammed  down  solid  after  the  connections 
are  made,  and  the  pipe  at  this  point  should  be  supported  on  sound 


483 


18 


PLUMBING. 


wooden  blocks.  If  galvanized  iron  is  used  for  the  service  pipe,  it 
should  in  all  cases  be  connected  to  the  main  service  cock  with  a 
short  piece  of  lead  pipe  two  or  three  feet  long,  for  the  reason  that 
lead  will  give  or  sag  with  the  pressure  of  the  earth  without  break- 
ing. The  remainder  of  the  pipe  should  be  carefully  embedded  in 
the  earth,  to  prevent  uneven  strains  at  any  particular  point. 
Connections  between  the  lead  and  iron  pipes  should  be  made  by 
means  of  brass  ferrules  and  wiped  joints.  A  stopcock  should 
be  placed  in  the  service  pipe  just  inside  the  cellar  wall,  and  in  a 
position  where  it  will  be  accessible  in  case  of  accident.  A  drip 
should  be  connected  with  the  stopcock  for  draining  the  pipes 
when  water  is  shut  off. 

In  protecting  pipes  against 
freezing  it  is  well  to  pack  them 
in  hair,  felt,  granulated  cork  or 
dry  shavings  where  they  pass 
through  the  floor.  This  is  shown 
in  Fig.  8.  When  the  service 
pipe  comes  in  below  the  cellar 
floor,  it  may  be  arranged  as  shown 
in  Fig.  9.  The  cock  should  be 
placed  about  18  inches  below  the 
cellar  bottom  in  a  wooden  box 
with  hinged  cover,  so  that  it 
may  be  easily  reached. 
In  many  cities  and  in  certain  elevated  situations  the  pres- 
sure in  the  mains  is  not  sufficient  to  carry  the  water  to  the 
house  tanks  in  the  attics  of  the  higher  buildings,  and  it  becomes 
necessary  to  use  some  form  of  automatic  pump  for  this  purpose. 
The  screw  pump  shown  in  Fig.  10  is  especially  adapted  to  uses  of 
this  kind  when  equipped  with  an  electric  motor  and  automatic 
starting  and  stopping  devices.  A  float  in  the  tank  operates  an 
electric  switch  by  means  of  a  chain  and  weights,  as  shown.  A 
centrifugal  or  rotary  pump  is  also  satisfactory  for  this  work. 

Another  device  which  may  be  attached  to  a  steam  pump  is 
shown  in  Fig.  11.  When  the  water  line  in  the  tank  reaches 
a  given  height,  the  aoat  closes  a  butterfly  valve  in  the 
discharge  pipe,  thus  increasing  the  pressure  within  it;  this 


484 


PLUMBING. 


19 


in  pressure  acts  on  the  bottom  of  a  piston  by  means  of  a  connect- 
ing pipe,  and  in  raising  the  piston,  shuts  off  the  steam  supply  to  the 
pump.  When  the  water  line  in  the  tank  is  lowered,  the  float  falls 

and  the  butteifly  valve 
opens,  relieving  the  pres- 
sure in  the  pipe  and  al- 
lowing the  steam  valve  to 
open  by  the  action  of  the 
counterweights  attached 
to  the  lever  arm  of  the 
valve,  as  shown.  The 
automatic  valve  is  shown 
in  section  in  Fig.  12. 
Another  means  of  rais- 
ing water  to  an  eleva- 
tion for  domestic  pur- 
poses, especially  in  the 
country,  is  by  the  use  of 
a  windmill.  A  large 
storage  tank  is  placed  at 
a  suitable  height  so  that 
a  sufficient  supply  may 
be  pumped  on  windy 
days  to  last  over  inter- 
vening periods  of  calm 
weather. 

HOT- WATER  SUPPLY. 

All  modern  systems 
of  plumbing  include  a 
hot-water  supply  to  the 
various  sinks,  bowls, 
bathtubs  and  laundry- 
tubs  throughout  the 
house. 


Fig.  10. 


Fig.  13  shows  the  usual  arrangement  of  a  kitchen  boiler  and 
water-back   with  the  necessary  pipe  connections.     The  boiler  is 


435 


20 


PLUMBING. 


Fig.  11. 


486 


PLUMBING. 


21 


commonly  made  of  copper  and  supported  upon  a  castriron  base. 
It  may  be  located  in  the  kitchen  near  the  range,  or  may  be 
concealed  in  a  nearby  closet.  The  "water-back,"  so  called,  is 
a  special  casting  placed  so  as  to  form  one  side  of  the  fire  box  in 


the  range.  The  cold-water  supply  pipe  to  the  boiler  usually 
enters  at  the  top  and  is  carried  down  to  a  point  near  the  bottom, 
as  shown  by  the  dotted  lines.  Connection  is  made  between  the 
bottom  of  the  boiler  and  the  lower  chamber  of  the  water-back.  The 
upper  chamber  is  connected  at  a  point  about  one-third  of  the  way 
up  in  the  side  of  the  boiler,  as  shown.  The  circulation  of  water 


487 


22 


PLUMBING. 


through  the  boiler  and  supply  pipes  is  the  same  as  already  de- 
scribed for  hot-water-heating  sj-stems.  The  range  fire  in  contact 
with  the  water-back  heats  the  water  within  it,  which  causes  it  to 
rise  through  the  pipe  connected  witli  the  upper  chamber  and 


HOT  WATER    TO  BU/LD/NG 


COLO   WATER 
SUPPLY 


Ai Jt 11 


WATER    BACK. 
/N  RANGE 


Fig.    13. 

flow  into  the  boiler  or  tank ;  in  the  meantime  cooler  water  flows 
in  at  the  lower  connection  to  take  its  place,  and  the  circulation 
thus  set  up  is  constant  as  long  as  there  is  a  fire  in  the  range. 

The  "boiler,"  so  called,  is  not  a  heater,  but  only  a  storage 
tank.  As  the  water  becomes  heated  it  rises  to  the  top  of  the  tank 
and  is  carried  to  the  different  fixtures  in  the  building  through  a 
pipe  or  pipes  connected  at  this  point.  The  cold-water  supply  pipe 
is  connected  with  the  house  tank  so  that  the  pressure  in  the  boiler 


488 


PLUMBING. 


is  that  due  to  the  height  of  the  tank  above  it.  When  any  of  the 
hot-water  faucets  are  open^  the  pressure  of  the  cold  water  in  the 
supply  pipe  forces  out  the  hot  water  at  the  top  of  the  boilers 
and  rushes  in  to  take  its  place.  There  is  no  connection 
between  the  circulation  through  the  water-back  and  the  pressure 
in  the  cold-water  supply  pipe.  The  circulation  is  due  only  to  the 
difference  in  temperature  be- 
tween the  water  in  the  pipe 
leading  from  the  top  of  the 
water-back  and  the  water  in 
the  lower  part  of  the  boiler, 
and  difference  in  elevation  of 
the  connections  with  the 
boiler.  The  nearer  the  top  of 
the  boiler  the  discharge  from 
the  water-back  is  connected, 
the  more  rapid  will  be  the  BLOW^<. 
circulation  and  the  greater 
the  quantity  of  water  which 
will  be  heated  in  a  given 

time.  The  cold-water  supply  simply  furnishes  a  pressure  to  force 
the  hot  water  through  the  pipes  to  the  different  fixtures,  and  re- 
places any  water  that  is  drawn  from  the  boiler. 

Care  should  always  be  taken  to  have  the  pipes  between  the 
water  back  and  the  boiler  free  from  sediment  or  any  other  ob- 
struction. If  the  water-back  from  any  cause  should  become  shut 
off  from  the  boiler,  an  explosion  would  be  likely  to  occur  if  there 
was  a  hot  fire  in  the  range.  Freezing  of  the  pipes  is  sometimes  a 
cause  of  accident.  The  sediment  which  accumulates  more  or  less 
rapidly  should  be  regularly  blown  off  through  the  blow-off  cock 
provided  for  this  purpose  at  the  bottom  of  the  boiler.  The  best 
time  for  doing  this  is  in  the  morning,  before  the  fire  is  started. 
The  device  shown  in  Fig.  14  is  intended  to  prevent  the  sediment 
from  collecting  in  the  pipes  or  from  being  drawn  into  the  water- 
back,  making  the  water  roily  when  a  large  amount  is  drawn  off  at 
one  time.  It  consists  of  a  smaU  cylinder  or  chamber  connected 
to  the  bottom  of  the  boiler  in  such  a  way  that  the  sediment  will 
fall  into  it  and  not  be  disturbed  by  the  circulation  of  the  water 
through  the  pipes. 


Fig.  14. 


489 


24 


PLUMBING. 


Double  Water-back  Connections.  It  is  often  desirable  to 
connect  a  boiler  with  two  water-backs,  one  in  the  kitchen  range 
and  another  in  a  laundry  stove  in  the  cellar  for  summer  use. 
Fig.  15  shows  the  common  method  of  making  the  connections. 
In  this  case  either  may  be  used  separately,  or  both  together  with- 
out any  adjustment  of  valves.  The  blow-off  cock  at  the  bottom 


Fig.  15. 

of  the  lower  water-back  should  be  opened  quite  often  to  clear  it 
of  sediment,  as  it  will  collect  much  faster  at  this  point  than  at  the 
bottom  of  the  boiler. 

Double  Boiler  Connections.  It  quite  frequently  happens  that 
the  kitchen  boiler  does  not  have  sufficient  capacity  for  the  entire 
house,  and  it  is  not  desirable  to  use  a  larger  boiler  on  account 


490 


PLUMBING. 


26 


V    I    / 


of  the  limited  space  in  the  kitchen.  In  such  cases  a  second  boiler 
may  be  connected  with  the  laundry  stove  if  one  is  provided,  and 
the  water  pipes  from  both  boilers  be  connected  together  at  some  point 
so  that  they  may 
both  discharge  hot 
water  into  the  same 
general  supply. 

Stopcocks  should 
be  placed  in  the 
pipe  connections  as 
shown,  so  that 
either  boiler  may 
be  shut  off  for 
repairs  without  in- 
terfering with  the 
operation  of  the 
other.  Waste  cocks 
should  always  be 
used  for  this  pur- 
pose, so  that  when 
closed  there  will 
be  a  connection  be- 
tween the  boiler 
and  the  atmos- 
phere. This  will 
prevent  damage  to 
the  boiler  in  case 
those  in  charge 
should  forget  to 
open  the  cocks 
when  starting  up  a 
fire  in  the  stove 
with  which  the 
boiler  is  connected. 


V  —  1 

1 

\ 

] 

Fig.  16. 


Circulation  Pipes.  It  is  often  desirable  to  produce  a  con- 
tinuous circulation  in  the  distributing  pipes  so  that  hot  water  may 
be  drawn  from  the  faucets  at  once,  without  waiting  for  the  cooler 
water  in  the  pipe  between  the  boiler  and  the  faucet  to  run  out. 


491 


26 


PLUMBING. 


This  is  accomplished  by  connecting  a  small  pipe  with  the  hot- 
water  pipe  near  the  faucet,  and  connecting  it  with  the  bottom  of 
the  boiler  as  shown  in  Fig.  17.  This  makes  a  circuit,  and  a  con- 
stant circulation  is  produced  by  the  difference  in  temperature  of 
the  water  in  the  supply  and  circulation  pipes. 


TER     SUPPLY 


Fig. 


Ripe  Connections*  Brass  or  copper  pipe  with  screwed  fit- 
tings should  always  be  used  for  making  the  connections  between 
the  boiler  and  water  back.  Where  unions  are  used  they  should 
have  ground  joints  without  packing.  Lead  pipe  is  too  soft  to 


492 


PLUMBING. 


27 


stand  the  high  temperature  to  which  these  pipes  are  sometimes 
subjected. 

Laundry  Boilers.  In  laundries,  hotels,  etc.,  where  a  large 
amount  of  hot  water  is  used,  it  is  necessary  to  have  a  larger 
storage  tank  and  a  heater  with  more  heating  surface  than  can  be 


Fig.  18. 

obtained  in  the  ordinary  range  water-back.      Fig.  18    shows  an 
arrangement  for  this  purpose. 

The  boiler  may  be  of  wrought  iron  or  steel  of  any  size  de- 
sired, and  is  usually  suspended  from  the  ceiling  by  means  of 
heavy  strap  iron.  The  heaters  used  are  similar  to  those  employed 
for  hot  water  warming.  The  method  of  making  the  connections 
is  indicated  in  the  illustration. 


493 


PLUMBING. 


The  capacity  of  the  heater  and  tank  depends  entirely  upon 
the  amount  of  water  used.  In  some  eases  a  large  storage  tank 
and  a  comparatively  small  heater  are  preferable^  and  in  others 
the  reverse  is  more  desirable. 

The  required  grate  surface  of  the  heater  may  be  computed  as 
fallows  :  first  determine  or  assume  the  num"ber  of  gallons  to  be  heated 
per  hour,  and  the  required  rise  in  temperature.  Reduce  gallons 


STEAM   CO/L 


COLO     WATER 
SUPPLY 


Fig.  19 

to  pounds  by  multiplying  by  8.3,  and  multiply  the  result  by  the 
rise  in  temperature  to  obtain  the  number  of  thermal  units.  As- 
suming a  combustion  of  five  pounds  of  coal  per  square  foot 
of  grate,  and  an  efficiency  of  8,000  thermal  units  per  pound 
of  coal,  we  have 


Grate  Surface  in  sq.  ft.  =  g^L^L^H  X  8.3  X  rise  intemp^ 

o  X  8,000 

Example. —  How  many  square  feet  of  grate  surface  will  be 
required  to  raise  the  temperature  of  200  gallons  of  water  per 
hour  from  40  degrees  to  180  degrees  ? 

2QOX8.3_X_(180-40) 

5  X  8000 

In  computing  the  amount  of  water  required  for  bathtubs  it 
is  customary  to  allow  from  20  to  30  gallons  per  tub,  and  to  con- 


494 


PLUMBING. 


29 


0^55=3 


sider  that  the  tub  may  be  used  three  or  four  times  per  hour  as  a 
maximum  during  the  morning.  This  will  vary  a  good  deal,  de- 
pending upon  the  character  of  the  building.  The  above  figures 
are  based  on  apartment  hotel  practice. 

Boilers  with  Steam  Coils.  In  large  buildings  where  steam 
is  available,  the  water  for  domestic  purposes  is  usually  warmed  by 
placing  a  steam  coil  of  brass  or 
copper  pipe  in  the  storage  tank. 
This  may  be  a  trombone  coil  made 
up  with  brass  fittings,  or  a  spiral 
consisting  of  a  single  pipe.  Heaters 
of  these  types  are  shown  in  Figs. 
19  and  20.  The  former  must  be 
used  in  tanks  which  are  placed 
horizontally,  and  the  latter  in 
vertical  tanks.  If  the  steam  is 
used  at  boiler  pressure,  the  con- 
densation may  return  directly  to 
the  boiler  by  gravity ;  but  if  steam 
at  a  reduced  pressure  is  used,  it 
must  be  trapped  to  the  receiver  of 
a  return  pump  or  to  the  sewer. 

The  cold  water  is  supplied 
near  the  bottom  of  the  tank,  and 
the  service  pipes  are  taken  off 
at  the  top.  A  drip  pipe  should 

be  connected  with  the  bottom,  for  draining  the  tank  to  the 
sewer.  Gate  valves  should  be  provided  in  all  pipe  connections 
for  shutting  off  in  case  of  repairs.  Sometimes  a  storage  tank  is 
connected  with  a  steam-heating  system  for  winter  use,  and  cross 
connected  with  a  coal-burning  heater  for  summer  use  where 
steam  is  not  available.  Such  an  arrangement  is1  shown  in 
Fig.  21. 

The  efficiency  of  a  steam  coil  surrounded  by  water  is  much 
greater  than  when  placed  in  the  air.  A  brass  or  copper  pipe  will 
give  off  about  200  thermal  units  per  square  foot  of  surface  per 
hour  for  each  degree  difference  in  temperature  between  the  steam 
and  the  surrounding  water.  This  is  assuming  that  the  water  is 


COLD   WAT£R 
SUPPLY 


Fig.  20. 


30 


PLUMBING. 


circulating  through  the  heater  so  that  it  moves  over  the  coil  at  a 
moderate  velocity.  In  assuming  the  temperature  of  the  water  we 
must  take  the  average  between  that  at  the  inlet  and  outlet. 

Example. —  How  many  square  feet  of  heating  surface  will  be 
required  in  a  brass  coil  to  heat  100  gallons  of  water  per  hour 
from  38  degrees  to  190  degrees,  with  steam  at  5  pounds  pressure? 


Fig.  21. 


Water  to  be  heated  =  100  X  8.3  =  830  pounds. 
Rise  in  temperature  —  190  —  38  =  152  degrees. 
Average  temperature  of  water  in  contact  with  the  coils 


190 


—  114  degrees 


496 


PLUMBING. 


31 


Temperature  of  steam  at  5  pounds  pressure  :=  228  degrees. 
The  required  B.  T.  U.  per  hour  =  830  X  152  =  120,160. 
Difference  between  the  average  temperature  of  the  water  and 
the  temperature  of  the  steam  =  228  — 114  =  114  degrees. 

B.  T.  U.  given  up  to  the  water  per  square  foot  of  surface  per 
hour  =  114  X  200  =  22,800,  and 
126,160 
22,800 


=r  5.5  square  feet.     Ans. 


EXA/1PLES  FOR  PRACTICE. 

1.  How  many  linear 
feet  of  1-inch  brass  pipe  will 
be  required  to  heat  150  gal- 
lons of  water  per  hour  from 
40  to  200  degrees,  with  steam 
at  20  pounds  pressure  ? 

Ans.  21.8  feet. 

2.  How   many    square 
feet  of  grate  surface  will  be 
required  in  a  heater  to  heat 
300  gallons  of  water  per  hour 
from  50  to  170   degrees? 

Ans.  7.4  square  feet. 

3.  A  hot-water  storage 
tank    has  a  steam    coil  con- 
sisting of   30  linear   feet   of 
1-inch    brass    pipe.         It   is 
desired  to  connect  a  coal-burn- 
ing heater   for   summer   use 
which    shall  have   the   same 
capacity.    Steam  at  5  pounds 
pressure    is    used,    and    the 
water  is  raised  from  40  to  180 
degrees.     How  many  square 
feet  of  grate  surface  are    re- 
quired? Ans.  5.9  sq.  ft. 

4.  A   hotel    has  30  bathtubs,   which  are  used  three  timep 
apiece  between  the  hours  of  seven  and  nine  in  the  morning.     The 


Fig.  22. 


497 


32 


PLUMBING. 


hot-water  system  has  a  storage  tank  of  400  gallons.  Allowing  20 
gallons  per  bath,  and  starting  with  the  tank  full  of  hot  water,  how 
many  square  feet  of  grate  surface  will  be  required  to  heat  the 
additional  quantity  of  water  within  the  stated  time,  if  the  temper- 
ature is  raised  from  50  to  130  degrees?  If  steam  at  10  pounds 
pressure  is  used  instead  of  a  heater,  how  many  square  feet  of 
heating  coil  will  be  required?  .  j  11. (>  sq.  ft.  grate. 

I  1.5.:)  sq.  ft.  coil. 

Temperature  Regulators.  Hot-water  storage  tanks  having 
special  heaters  or  steam  coils  snould  be  provided  with  some  means 
for  regulating  the  temperature  of  the  water.  Fig.  22  shows  ;i 
simple  form  attached  to  a  coal-burning  heater.  It  consists  of  a 


Fig.  23. 

casting  about  nine  inches  long,  tapped  at  the  ends  to  receive  a 
2-inch  pipe,  and  containing  within  it  a  second  shell  called  the 
steam  generator.  (See  Fig.  28.)  The  outer  shell  is  connected 
with  the  circulation  pipe  as  shown  in  Fig.  22.  The  generator  is 
filled  with  kerosene,  or  a  mixture  of  kerosene  and  water,  depend- 
ing upon  the  temperature  at  which  it  is  wished  to  have  the  regu- 
lator operate.  The  inner  chamber  connects  with  the  space  below 
a  flexible  rubber  diaphragm.  The  boiling  point  of  the  mixture  in 
the  generator  is  lower  than  that  of  water  alone,  and  depends  upon 
the  proportion  of  kerosene  used,  so  that  when  the  temperature 
of  the  water  in  the  outer  chamber  reaches  this  point,  the  mixture 
boils,  and  its  vapor  creates  a  pressure  which  forces  down  the 
diaphragm  and  closes  the  draft  door  of  the  heater  with  which  it 
is  connected - 


498 


PLUMBING. 


33 


A  form  of  regulator  for  use  with  a  steam  coil  is  shown  iw 
Fig.  24.  This  consists  of  a  rod  made  up  of  two  metals  having 
different  coefficients  of  expansion,  and  so  arranged  that  this  differ- 
ence in  expansion  will  produce  sufficient  movement,  when  the 
water  reaches  a  given  temperature,  to  open  a  small  valve.  This 


Fig.  24. 

allows  water  pressure  from  the  street  main  with  which  it  is  con- 
nected, to  flow  into  a  chamber  above  a  rubber  diaphragm,  thus 
closing  the  steam  supply  to  the  coil.  When  the  water  cools,  the 
rod  contracts',  and  the  pressure  is  released  above  the  diaphragm, 
allowing  the  valve  to  open  and  thus  again  admit  steam  to  the 
coil. 


34  PLUMBING. 


GAS    FITTING. 

Next  to  heating  and  ventilation  and  plumbing  there  is  uo 
part  of  interior  house  construction  requiring  so  much  attention  as 
the  gas  piping  and  gas  fitting. 

Gas  piping  in  buildings  should  be  installed  according  to 
carefully  drawn  specifications,  and  only  experienced  workmen 
should  be  employed.  The  gas  fitter  should  work  from  an  accurate 
sketch  plan  showing  the  location  of  all  gas  service  and  distributing 
pipes  in  the  building  and  the  locations  of  the  meter  and  shut-off 
cock.  The  plan  should  also  indicate  the  exact  location  and  size 
of  the  risers  and  the  position  of  the  lights  in  the  different  rooms. 

Service  Pipe  and  Meter.  The  service  pipe  by  which  the  gas 
is  conveyed  to  a  building  is  always  put  in  by  the  gas  company. 
The  size  of  tins  pipe  is  governed  by  the  number  of  burners  to  be 
supplied,  but  it  should  never  in  any  case,  even  for  the  smallest 
house,  be  less  than  1  inch  in  diameter.  This  may  be  slightly 
larger  than  is  necessary,  but  the  cost  is  only  a  little  more  and  the 
liability  of  stoppages  is  much  less ;  this  also  allows  for  the  future 
addition  of  more  burners,  which  is  often  a  matter  of  much  con- 
venience. Service  and  distributing  pipes  for  water,  or  naphtha 
gas,  should  be  from  15  to  20  per  cent  larger  than  for  coal  gas. 
The  material  for  the  main  service  pipe,  from  the  street  to  the 
house,  should  be  either  lead  or  wrought  iron.  As  a  rule,  wrought- 
iron  pipe  with  screwed  joints  is  preferable  to  lead,  because  it  is 
less  likely  to  sag  in  the  trench,  thus  causing  dips  for  the  accumu- 
lation of  water  of  condensation.  Care  must  be  observed  in  the 
use  of  wrought-iron  pipe  to  protect  it  by  coating  with  asphalt,  or 
coal  tar,  to  prevent  corrosion.  The  pipe  should  also  be  well  sup- 
ported in  the  trench.  Service  pipes  should  preferably  rise  from 
the  street  gas  main  toward  the  house  in  order  to  allow  all  conden- 
sation to  run  back  into  the  mains.  This,  however,  cannot  always 
be  done,  owing  to  the  relative  levels  of  the  street  main  and  the 
meter  in  the  house.  The  latter  should  be  placed  in  a  cool,  well- 
lighted  position,  at  or  below  the  level  of  the  lowest  burner,  which 
is  usually  in  the  cellar.  If  the  meter  is  below  the  gas  main,  the 
service  pipe  must  grade  toward  the  house  and  should  be  provided 
with  a  drip  pipe,  or  "siphon,"  before  connecting  with  the  meter. 


500 


PLUMBING.  35 


When  water  accumulates  in  the  siphon,  the  cap  is  removed  and 
the  pipe  drained.  The  gas  company  usually  supplies  and  sets  the 
meter,  which  should  be  of  ample  size  for  the  number  of  lights 
burned. 

A  stopcock,  or  valve,  is  placed  by  the  company  in  the  service 
pipe,  so  that  the  gas  may  be  shut  off  from  each  building  sepa- 
rately. This  is  usually  placed  outside  near  the  curb  in  the  case 
of  buildings  requiring  a  pipe  11  inches  in  diameter,  or  larger.  In 
the  case  of  theaters  or  assembly  halls  it  is  often  required  by  law 
as  a  safeguard  in  case  of  fire.  The  meter  is  connected  with  both 
the  service  pipe  and  the  main  house  pipe  by  means  of  short  con- 
nections of  extra  heavy  lead  pipe.  A  cock  is  placed  near  the 
meter,  and  in  large  buildings  this  is  arranged  so  that  a  lock  may 
be  attached  to  it  when  the  gas  is  shut  off  by  the  company.  Gate 
valves  are  preferable  for  gas  mains,  as  they  give  a  free  opening 
equal  to  the  full  size  of  the  pipe. 

PIPES. 

Distributing  Pipes.  The  distributing  pipes  inside  of  a  house 
are  usually  of  wrought  iron,  except  where  exposed  in  rooms,  or 


Fig.  25.  Fig.  26.  Fig.  27.  Fig.  28. 

carried  along  walls  lined  with  enameled  brick,  or  tile,  in  which 
case  they  may  be  of  polished  bass,  or  copper.  The  chief  re- 
quirements for  wrought-iron  distributing  pipes  are  that  they  be 
carefully  welded  and  perfectly  circular  in  section.  The  first  is 
important  in  order  to  avoid  splitting  when  cutting  or  threading 
them  on  the  pipe  bench. 

All  gas  pipes  are  put  together  with  screwed  joints,  a  thread 
'being  cut  upon  the  outside.  When  the  pipe  is  irregular  in  sec- 
tion the  threading  will  be  more  or  less  imperfect,  and  as  a  result 
the  joints  will  be  defective.  A  good  gas  fitter  must  examine  all 
pipe  as  it  is  delivered  at  the  building,  and  observe  the  section 


501 


PLUMBING. 


either  by  means  of  the  eye  or  by  the  use  of  calipers.  Plain 
wrought-iron  pipe  is  likely  to  rust  upon  the  inside,  especially 
where  the  gas  supplied  is  imperfectly  purified,  and  for  this  reason 
it  is  often  advisable  to  use  rustless,  or  galvanized  pipe,  for  the 
smaller  sizes. 


Fig.  29. 

Fittings  and  Joints.      The  fittings   used  in  gas  piping  are 

similar  to  those  employed  in  steam  work,  such  as  couplings, 
elbows,  tees,  crosses,  etc.  (see  Figs.  25,  26,  27  and  28).  Other 
fittings  not  so  extensively  used  are  the  union,  the  flange  union, 

the  running  socket  and  right 
and  left  couplings.  Fig.  29 
shows  a  screwed  union  and 
Fig.  30  a  flange.  These  fit- 
tings are  of  cast  iron,  or  of 
malleable  iron,  the  latter  being 
preferred  for  the  smaller  sizes. 
Fittings  may  be  either  gal- 
vanized, or  rustless,  as  in  the 


Fig.  30. 


case  of  pipe,  and  it  is  especially  necessary  that  they  be  free  from 
sand  holes.  In  making  pipe  joints  the  gas  fitter  should  make  use 
of  red  lead,  or  red  and  white  lead  mixed,  to  make  up  for  any  pos- 
sible imperfections  in  the  threads ;  this,  however,  should  be  used 
sparingly  so  that  the  pipe  may  not  be  choked  or  reduced  in  size. 
The  use  of  gas  fitters'  cement  should  be  prohibited.  It  is  impor- 
tant that  each  length  should  be  tightly  screwed  into  the  fitting 
before  the  next  length  is  put  on.  It  is  always  a  wise  precaution 


5C3 


PLUMBING.  37 


to  examine  eacli  length  of  pipe  before  it  is  put  in  place,  to  inakt; 
sure  it  is  free  from  imperfections  of  any  kind. 

Running  Pipes  and  Risers.  All  large  risers  should  be  ex- 
posed, and  it  is  desirable  to  keep  all  piping  accessible  aa  far  as 
possible  so  that  it  may  be  easily  reached  for  repairs.  All  hori- 
zontal pipes  should  be  run  with  an  even  though  slight  grade 
toward  the  riser,  and  all  sags  in  the  pipes  must  be  avoided  to  prevent 
the  collection  of  water,  and  for  this  reason  they  should  be  well  sup- 
ported. Floor  boards  over  all  horizontal  pipes  should  be  fastened 
down  with  screws  so  that  they  may  be  removed  for  inspection  of  the 
pipes.  When  it  becomes  necessaiy  to  trap  a  pipe,  a  drip  with  a 
dram  cock  must  be  put  in,  but  this  should  always  be  avoided  un- 
der floors  or  in-  other  inaccessible  places.  When  pipes  under  floors 
run  across  the  timbers,  the  latter  should  be  cut  into  near  the  ends, 
or  where  supported  upon  partitions,  in  order  to  avoid  weakening 
the  timbers.  All  branch  outlet  pipes  should  be  taken  from  the 
side  or  top  of  the  running  lines,  and  bracket  pipes  should  be  run 
up  from  below  instead  of  dropping  from  above.  Never  drop  a 
center  pipe  from  the  bottom  of  a  running  line ;  always  take  such 
an  outlet  from  the  side  of  the  pipe.  Where  possible  it  is  better 
to  cany  up  a  main  riser  near  the  center  of  the  building,  as  the 
distributing  pipes  will  be  smaller  than  if  carried  up  at  one  end. 
Where  this  is  done  the  timbers  will  not  require  so  much  cutting, 
and  the  flow  of  gas  will  be  more  uniform  throughout  the  system. 

When  a  building  has  different  heights  of  post  it  is  always 
better  to  have  an  independent  riser  for  each  height  rather  than  to 
drop  a  system  of  piping  from  a  higher  to  a  lower  post  and  grading 
to  a  lower  point  and  establishing  drip  pipes.  Drips  in  a  building 
should  be  avoided  if  possible  and  the  whole  system  of  piping  be 
so  arranged  that  any  condensed  gas  will  flow  back  through  the 
system  and  into  the  service  pipe.  All  outlet  pipes  should  be 
securely  fastened  in  position,  so  that  there  will  be  no  possibility 
of  their  moving  when  the  fixtures  are  attached.  Center  pipes 
should  rest  on  a  solid  support  fastened  to  the  floor  timbers  near 
the  top.  The  pipe  should  be  securely  fastened  to  the  support 
to  prevent  movement  sidewise.  The  drop  must  be  perfectly  plumb 
and  pass  through  a  guide  fastened  near  the  bottom  of  the  timbers 
in  order  to  hold  it  rigidly  in  position.  (See  arrangement,  Fig.  31.) 


503 


38 


PLUMBING. 


Unless  otherwise  directed,  outlets  for  brackets  should  be 
placed  5|-  feet  from  the  floor  except  in  the  cases  of  hallways  and 
bathrooms,  Avhere  it  is  customary  to  place  them  6  feet  from  the 
floor.  Upright  pipes  should  be  plumb,  so  that  nipples  which  pro- 
ject through  the  walls  will  be  level;  the  nipples  should  not 


Fig.  31. 

project  more  than  |  inch  from  the  face  of  the  plastering.  Lathes 
and  plaster  together  are  usually  about  |  inch  thick,  so  the  nipples 
should  project  about  1-i  inches  from  the  face  of  the  studding. 

Gas  pipes  should  never  be  placed  on  the  bottoms  of  floor 
timbers  that  are  to  be  lathed  and  plastered,  because  they  are  inac- 
cessible in  case  of  leakage  or  alterations. 

Pipe   Sizes.      All    risers    and    distributing    pipes,    and    all 


504 


PLUMBING. 


branches  to  bracket  and  center  lights  should  be  of  sufficient  size 
to  supply  the  total  number  of  burners  indicated  on  the  plans. 
Mains  and  brandies  should  be  proportioned  according  to  the  num- 
ber of  lights  they  are  to  supply,  and  not  the  number  of  outlets. 

No  pipe  should  be  less  than  |  inch  in  diameter,  and  this  size 
should  not  be  used  for  more  than  two-bracket  lights.  No  pipe 
for  a  chandelier  should  be  less  than  1  inch  up  to  four  burners, 
and  it  should  be  at  least  |  inch  for  more  than  four  burners.  The 
following  table  gives  sizes  of  supply  pipes  for  different  numbers 
of  burners  and  lengths  of  run. 

TABLE  VII. 


Size  of  Pipe. 
Inches. 

Greatest  Length 
of  Run. 
Feet. 

Greatest    Num- 
ber of    Burners 
to  be  Supplied. 

f 

20 

2 

30 

4 

£ 

50 

15 

1 

70 

25 

1| 

100 

40 

H 

150 

70 

2 

200 

140 

2* 

300 

225 

3 

400 

300 

4 

500 

500 

Testing  Gas  Pipes.  As  soon  as  the  piping  is  completed,  it 
should  be  tested  by  means  of  an  air  pump  ;  a  manometer  or  mer- 
cury gage  is  used  to  indicate  the  pressure.  In  the  case  of  large 
buildings,  it  is  better  to  divide  the  piping  into  sections,  and  test 
each  separately.  All  leaks  revealed  must  be  repaired  at  once,  and 
the  test  repeated  until  the  whole  system  is  air  tight  at  a  pressure 
of  from  15  to  20  inches  of  mercury,  or  7J  to  10  pounds  per 
square  inch. 

The  final  test  is  of  great  importance.  This  test  is  to  provide 
against  future  troubles  and  dangers  from  leaks  resulting  from 
sand  holes  in  the  fittings,  split  pipe,  imperfect  threads,  loose  joints 
or  outlets  left  without  capping.  If  the  building  is  new,  a  careful 
inspection  should  first  be  made  to  see  that  all  outlets  are  closed, 
then  the  valve  in  the  service  pipe  closed  and  the  air  pump  at- 
tached to  any  convenient  side-light.  To  the  same  outlet  or  an 


505 


40  PLUMBING. 


adjacent  one  attach  the  mercury  column  gage  used  by  gas.  fitters, 
and  having  a  column  from  15  to  20  inches  in  height.  Care  must 
be  taken  that  there  are  no  leaks  in  the  gage  or  its  connections ;  a 
tight-closing  valve  must  be  placed  between  the  gas  pipe  and  the 
temporary  connections  with  the  pump,  so  that  it  may  be  shut  off 
immediately  after  the  pump  stops,  thus  preventing  any  leakage 
through  the  pump  valves  or  hose  joints.  When  all  is  ready, 
pump  the  system  full  of  air  until  the  mercury  rises  to  a  height  of 
at  least  12  inches  in  the  gage;  then  close  the  intermediate  valve 
between  the  pump  and  the  piping.  Should  the  mercury  column 
"  stand  "  for  five  minutes,  it  is  reasonable  to  assume  that  the  pipes 
are  sufficiently  tight  for  any  pressure  to  which  they  will  afterward 
be  subjected. 

If  the  mercury  rises  and  falls  with  the  strokes  of  the  pump, 
it  indicates  a  large  leak  or  open  outlet  near  the  pump.  But 
should  there  be  a  split  pipe  or  an  aggregation  of  small  leaks,  the 
mercury  will  run  back  steadily  between  the  strokes  of  the  pump, 
though  more  slowly  than  it  rose.  Should  it  rise  well  in  the  glass 
and  sink  at  the  rate  of  1  inch  in  five  seconds,  small  leaks  in  fit- 
tings or  joints  may  be  expected. 

A  leak  that  cannot  be  detected  by  the  sound  of  issuing  air 
may  usually  be  found  by  applying  strong  soap-water  with  a  brush 
over  suspected  joints  or  fittings ;  the  leak  in  this  case  being  indi- 
cated by  the  bubbles  blown  by  the  escaping  air.  Sometimes  it  is 
necessary  to  use  ether  in  the  pipes  for  locating  leaks,  if  the  pipes 
i\re  in  partitions  or  under  floors.  The  ether  is  put  into  a  bend  of 
the  connecting  hose,  or  in  a  cup  attached  to  the  pump,  and  forced 
in  with  the  air.  By  following  the  lines  of  the  pipe,  the  approxi- 
mate position  of  a  leak  may  be  determined  by  the  odor  of  escap- 
ing ether. 

If  the  house  is  an  old  one  or  has  been  finished,  the  meter 
should  be  taken  .out  and  the  bottom  of  the  main  riser  capped. 
Next  remove  all  fixtures  and  cap  the  outlets.  Then  use  ether  to 
locate  the  leaks  before  tearing  up  floors  or  breaking  partitions. 

GAS  FIXTURES. 

Burners.  Illuminating  gas  is  a  complex  mixture  of  gases, 
of  which  various  chemical  compounds  of  carbon  and  hydrogen 


506 


PLUMBING.  41 


form  the  principal  light-giving  properties.  Gas  always  contains 
more  or  less  impurities,  such  as  carbonic  oxide,  carbonic  acid, 
ammonia,  sulphureted  hydrogen  and  bisulphides  of  carbon. 
These  are  partly  removed  by  purifying  processes  before  the  gas 
leaves  the  works. 

When  the  gas-jet  is  lighted,  the  hydrogen  is  consumed  in  the 
lower  part  of  the  flame,  producing  sufficient  heat  to  render  the 
minute  particles  of  carbon  incandescent.  The  hydrogen,  in  the 
process  of  combustion,  combines  with  the  oxygen  from  the  air, 
forming  an  invisible  vapor  of  water,  while  the  carbon  unites  with 
the  oxygen,  forming  carbonic  acid. 


Fig.  32.  Fig.  33.  Fig.  34. 

Various  causes  tend  to  render  combustion  incomplete :  there 
may  be  excessive  pressure  of  gas,  lack  of  air  or  defective  burners. 
An  excess  of  pressure  at  the  burners  causes  a  reduction  of  the 
amount  of  illumination ;  on  the  other  hand,  if  the  pressure  is  in- 
sufficient, the  heat  of  the  flame  will  not  raise  the  carbon  to  a 
white  heat,  and  the  result  will  be  a  smoky  flame.  It  therefore 
follows  that  for  every  burner  there  is  a  certain  pressure  and  corre- 
sponding flow  of  gas  which  will  cause  the  brightest  illumination. 

There  is  a  great  variety  of  burners  upon  the  market,  among 
which  the  following  are  the  principal  types : 

The  single-jet  burner,  the  bat's-wing  burner,  the  fish-tail 
burner,  the  Argand  burner,  the  regenerative  burner  and  the  in- 
candescent burner. 

The  Single-jet  burner  (Fig.  32)  is  the  simplest  kind,  having 


507 


42  PLUMBING. 


only  one  small  hole  from  which  the  gas  issues.     It  is   suitable 
only  where  a  very  small  flame  is  required. 

The  Batfs-wing  or  slit  burner  (Fig.  33)  has  a  hemispherical 
tip  with  a  narrow  vertical  slit  from  which  the  gas  spreads  out  in  a 
thin,  flat  sheet,  giving  a  wide  and  rather  low  flame,  resembling  in 
shape  the  wing  of  a  bat,  from  which  it  is  named.  The  common 
kind  of  slit  burners  are  not  suitable  for  use  with  globes,  as  the 
flame  is  likely  to  crack  the  glass. 

The  Union-jet  or  Fish-tail  burner  (Figs.  34   and  35)   consists 

_VL        f|f  a  flat  tip  slightly  depressed  or  concave  in  the  center, 

IPjL       with  two  small  holes  drilled,  as  shown  in  Fig.  35.     Two 

jajl      jets  of  equal  size  issue  from  these  holes,  and  by  impin- 

\          /      SmS  upon  each  other  produce  a  flat  flame  longer  and 

~ i      narrower  in  shape  than  the  bat's- wing,  and -not  unlike 

the  tail  of  a  fish.     Neither  of  these  burners  require  a 
chimney,  but  the  flames  are  usually  encased  with  glass  globes. 

The  Argand  burner  (Fig.  36)  consists  of  a  hollow  ring  of 
metal  connected  with  the  gas  tube,  and  perforated  oh  its  upper 
surface  with  a  series  of  fine  holes,  from  which  the  gas  issues, 
forming  a  round  flame.  This  burner  requires  a  glass  chimney. 
As  an  intense  heat  of  combustion  tends  to  increase  the  brilliancy 
of  the  flame,  it  is  desirable  that  the  burner  tips  shall  be  of  a  mate- 
rial that  will  cool  the  flame  as  little  as  possible.  On  this  account 


Fig.  37.  Fig.  38. 


metal  tips  are  inferior  to  those  made  of  some  nonconducting 
material,  such  as  lava,  adamant,  enamel,  etc.  Metal  tips  are  also 
objectionable  because  they  corrode  rapidly,  and  thus  obstruct  the 
passage  of  the  gas.  Figs.  37  and  38  show  lava  tips  •for  bat's- 
wing  and  fish-tail  burners.  Burner  tips  should  be  cleaned  occa- 


505 


PLUMBING. 


sionally,  but   care  should  be  taken  not  to  enlarge  the  slits  or 
holes. 

In  all  regenerative  burners  the  high  temperature  due  to  the 
combustion  in  a  gas  flame  is  used  to  raise  the  temperature  of  the 
gas  before  ignition,  and  of  the  air  before  combustion.  These 
powerful  burners  are  used  for  lighting  streets,  stores,  halls,  etc. 


Fig.  39. 


Fig.  40. 


In  the  incandescent  burner  the  heat  of  the  flame  is  applied  in 

raising  to  incandescence  some  foreign  material,  such  as  a  basket 

of  magnesium  or  platinum  wires,  or  a  funnel-shaped  asbestos  wick 

or   mantel    chemically  treated  with   sulphate  of  zirconium   and 

other  chemical  elements.     A  burner  of  this  kind 

is  shown  in  Fig.  39,  where  the  mantel  may  be 

seen  supported  over  the  gas  flame  by  a  wire  at 

the  side.     Fig.  40  shows  another  form  of  this 

burner  in  which  a  chimney  and  shade  are  used 

in  place  of  a  globe.     Burners  of  this  kind  give 

a  very  brilliant  white  light  when    used  with 

water  gas  unmixed  with  naphtha  gases.     The 

mantel,  however,  is  very  fragile,  and  is  likely 

to  lose  its  incandescence  when  exposed  to  an 

atmosphere  containing  much  dust. 

The  Bunsen  burner  shown  in  Fig.  41  is  a 
form  much  used  for  laboratory  work.  It  bums 
with  a  bluish  flame,  and  gives  an  intense  heat 
without  smoke  or  soot.  The  gas  before  ignition  is  mixed  with  a 
certain  quantity  of  air,  the  proportions  of  gas  and  air  being 
regulated  by  the  thumbscrew  at  the  bottom,  and  by  screwing  the 


Fig.  41. 


509 


44 


PLUMBING. 


outer  tube  up  or  down,  thus  admitting  a  greater  or  less  quantity 
of  air  at  the  openings  indicated  by  the  arrows.  This  same  principle 
is  utilized  in  a  burner  for  brazing,  the  general  form  of  which  is 


shown  in  Fig.  42. 
in  the  open  air. 


A  flame  of  this  kind  will  easily  melt  brass 


Fig.  42. 


Cocks.  It  is  of  greatest  importance  that  the  stopcocks  at 
the  fixtures  should  be  perfectly  tight.  It  is  rare  to  find  a  house 
piped  for  gas  where  the  pressure  test  could  be  successfully  ap- 
plied without  first  removing  the  fixtures,  as  the  joints  of  folding 


43. 


Fig.  44. 


brackets,  extension  pendants,  stopcocks,  etc.,  a/e  usually  found  to 
leak  more  than  the  piping.  The  old-fashioned,  "all-around"  cock 
should  never  be  allowed  under  any  conditions  whatever;  only 
those  provided  witli  stop  pins  should  be  used.  Various  forms  of 
cocks  with  stop  pins  are  shown  in  Figs.  43,  44  and  45.  All 


510 


PLUMBING. 


45 


joints  should  be  examined  and  tightened  up  occasionally  to  pre- 
vent tl<e:r  becoming  loose  and  leaky. 


Fig.  46. 


Fig.  47. 


Brackets  and  Chandeliers.  Poor  illumination  is  frequently 
caused  by  ill-designed  -or  poorly  constructed  brackets  or  chande- 
liers. Gas  fixtures,  almost  with- 
out exception,  are  designed  solely 
from  an  artistic  standpoint,  with- 
out regard  to  the  proper  condi- 
tions for  obtaining  the  best  illumi- 
nation. Fixtures  having  too  many 
scrolls  or  spirals  may,  in  the  case 
of  imperfectly  purified  gas,  accu- 


Fig.  45. 


Fig.  48. 


mulate  a  large  amount  of  a  tariy  deposit  which  in  time  hardens 
and  obstructs  the  passages.  Another  fault  is  the  use  of  very 
small  tubing  for  the  fixtures,  while  a  third  defect  consists  in 
the  many  leaky  stopcocks  of  the  fixtures,  caused  either  by  defec- 


46 


PLUMBING. 


tive  workmanship,  or  by  the  keys  becoming  worn  and  loose. 
Common  forms  of  brackets  are  shown  in  Figs.  46  and  47,  the  lat- 
ter being  an  extensive  bracket.  There  is  an  endless  variety  of 
chandeliers  used,  depending  upon  the  kind  of  building,  the  finish 
of  the  room  and  the  number  of  lights  required.  Figs.  48,  49  and 
50  show  common  forms  for  dwelling  houses,  Fig.  50  being  used 
for  halls  and  corridors. 


Fig.  50. 


Globes  and  Shades.  Next  to  the  burners,  the  shape  of  the 
globes  or  shades  surrounding  the  flame  affects  the  illuminating 
power  of  the  light.  In  order  to  obtain  the  best  results,  the  flow  of 
air  to  the  flame  must  be  steady  and  uniform.  Where  the  supply 
is  insufficient  the  flame  is  likely  to  smoke  ;  on  the  other  hand,  too 
strong  a  current  of  air  causes  the  light  to  flicker  and  become  dim 
through  cooling. 

Globes  with  too  small  openings  at  the  bottom  should  not  be 
used.  Four  inches  should  be  the  smallest  size  of  opening  for  an 
ordinary  burner.  All  glass  globes  absorb  more  or  less  light,  the 


518 


PLUMBING. 


47 


loss  varying  from  10  per  cent  for  clear  glass  to  60  per  cent  or 
more  for  colored  or  painted  globes.  Clear  glass  is  therefore  much 
more  economical,  although  where  softness  of  light  is  especially  de- 
sired the  use  of  opal  globes  is  made  necessary. 

COOKING    AND    HEATING    BY    GAS. 

Cooking  by  gas  as  well  as  heating  is  now  very  common  and 

there   is  a  great  variety  of  appliances    for  its   use  in   this  way. 

Cooking  by  gas  is  less  expensive  and  less  troublesome  than  by 

coal,  oil   or  wood   and  is 

more  healthful  on  account 

of    the    absence    of   waste 

heat,  smoke  and  dust.     A 

gas  range  is  always  ready 

for   use    and    is    instantly 

lighted  by   applying   a 

match  to  the  burner.     The  fire,  when  kindled,  is  at  once  capable 

of  doing  its  full  work ;  it  is  easily  regulated  and  can  be  shut  off 

the  moment  it  has  been 
used,  so  that  if  properly 
managed  there  is  no 
waste  of  fuel  as  in  the 
case  of  coal  or  wood. 
The  kitchen  in  the  sum- 
mertime may  be  kept 
comparatively  cool  and 
comfortable.  Gas  stoves 
are  made  in  all  sizes, 
from  the  simple  form 
shown  in  Fig.  51  to  the 
most  elaborate  range  for 
hotel  use.  A  range  for 

family  use,   with  ovens  and  water  heater,  is  shown  in  Fig.  52. 

Figs.  53  and  54  show  •  the  forms   of  burners  used  for  cooking, 

the    former   being   a  .griddle     burner     and    the    latter    an   oven 

burner. 

A  broiler  is  shown  in  Fig.  55 ;  the  sides  are  lined  with  asbes- 
tos, and  the  gas  is  introduced  through  a  large  number  of*  small 


Fig.  52. 


619 


48 


PLUMBING. 


openings.     The  asbestos  becomes  heated  and  the  effect  is  the  same 
as  a  charcoal  fire  upon  both  sides. 

Heating  by  Gas.     Gas  as  a  fuel  has  not  been  used  to  any 
great  extent  for  the  warming  of  whole  buildings,  its  application 


Fig.  54. 

being  usually  confined  to  the  heating  of  single  rooms.  Unlike 
cooking  by  gas,  a  gas  fire  for  heating  is  not  as  cheap  as  a  coal  fire 
when  kept  burning  constantly.  In  other  ways  it  is  effective  and 
convenient.  It  is  especially  adapted  to  the  warming  of  small 
apartments  and  single  rooms  where  heat  is  only  wanted  occasion- 


Fig.  53. 

ally  and  for  brief  periods  of  time. 
In  the  case  of  bedrooms,  bath- 
rooms or  dressing-rooms,  a  gas  fire 
is  preferable  to  other  modes  of 
warming  and  fully  as  economical. 
It  may  be  used  on  cold  winter  days 
as  a  supplementary  source  of  heat 
in  houses  heated  by  stoves  or  by 
furnaces.  Again,  a  gas  fire  may  be  used  as  a  substitute  for 
the  regular  heating  apparatus  in  a  house,  in  the  spring  or  fall,  when 
the  fire  in  the  furnace  or  boiler  has  not  yet  been  started.  It  is 
often  employed  as  the  only  means  for  heating  smaller  bedrooms, 
guest  rooms,  bathrooms,  and  for  temporary  heating  in  summer 
hotels  where  fires  are  required  only  on  occasional  cold  days. 

The  most  common  form  of  heater  is  that  shown  in  Fig.  56. 
This  is  easily  carried  from  room  to  room  and  may  be  connected 


514 


PLUMBING. 


49 


with  a  gas-jet,  after  first  removing  the  tip,  by  means  of  rubber 
tubing.  The  heater  is  simply  a  large  burner  surrounded  by  a 
sheet-iron  jacket  or  funnel.  Another  and  more  powerful  form  is 
the  gas  radiator,  shown  in  Fig.  57.  This  is  arranged  with  a 
flue  for  conducting  the  products  of  combustion  to  the  chimney,  as 
shown  in  the  section  Fig.  58.  Each  section  of  the  radiator  con- 
sists of  an  outer  and  an  inner  tube  with  the  gas  flame  between  the 


Fig.  56. 


Fig.  57. 


two.  This  space  is  connected  with  the  flue,  while  the  air  to  be 
heated  is  drawn  up  through  the  inner  tube,  as  shown  by  the 
arrows. 

Fig.  59  shows  an  asbestos  incandescent  grate,  and  Fig.  60  a 
grate  provided  with  gas  logs  made  of  metal  or  terra-cotta  and  as- 
bestos. The  gas  issues  through  small  openings  among  the  logs, 
and  giv3s  the  appearance  of  an  open  wood  fire. 

Hot-water  Heaters.  The  use  of  gas  cooking  ranges  makes  it 
necessary  to  provide  separate  means  for  heating  water.  This  is 
accomplished  in  several  ways.  The  range  shown  in  Fig.  52  has  a 
boiler  attached  which  is  provided  with  a  separate  burner. 

Fig.  ol  shows  a  gas  heater  attached  to  the  ordinary  Kitchen 


515 


f>0 


PLUMBING. 


boiler.  A  section  through  the  heater  is  shown  in  Fig.  62.  This 
consists  of  a  chamber  surrounded  by  an  outer  jacket  with  an  aii 
space  between.  Circulation  pipes,  through  which  the  water  passes, 
are  hung  in  the  inner  chamber  just  above  a  powerful  gas-burner 
placed  at  the  bottom  of  the  heater. 

A  heater  of  different  form  for  heating  larger  quantities  of 


Fig.  58. 


Fig.  60. 

water  is  shown  in  Figs.  63  and  64.  This  consists,  as  :n  the  c^se 
just  described,  of  a  circulation  coil  suspended  above  a  series  of 
burners,  '"he  supply  of  gas  admitted  to  the  burners  is  regulated 
by  r,n  automatic  valve,  which  is  opened  more  or  less  as  the  fio\\  of 
wat*3:  through  the  heater  is  increased  or  diminished.  When  no 


516 


PLUMBING. 


61 


water  is  being  used,  the  gas  is  shut  off  from  the  burners,  and  only 
a  small  "pilot  light/'  which  takes  its  supply  from  above  the  auto- 
matic valve,  is  left  burning.  As  soon  as  a  faucet  in  any  part  of 
the  building  is  opened  and  a  flow  of  water  started  through  the 
heater,  the  automatic  valve  opens,  admitting  gas  to  the  main  burn- 


OUTLET 


W/TH 

ASBESTOS 
L/N/NG 

SHEET  /RO 
JACKET  W/T 
ASBESTOS 
L/N/NG 

DEAD  A/f? 


SPACE 


LD  WATER 
K^BUM      CHAMBER 
VL    J    -HOT  WATER 
*     CHAMBER 


COLD  WATER 
-HOT  WATER 


COLO  WATER 
/NLET 


Fig.  61. 


Fig.  62. 

ers,  which  is  ignited  by  the  pilot  light,  and  in  a  few  moments  hot 
water  will  flow  from  the  faucet.  The  heater  shown  has  a  capacity 
of  9  gallons  per  minute  from  a  temperature  of  55  to  130°. 

Another  type  is  that  known  as  the  instantaneous  water  heater, 
one  form  of  which  is  shown  in  Fig.  65.  This  is  made  especially 
for  bathrooms,  and  will  produce  a  continuous  stream  of  hot  water 
whenever  desired.  The  heater  is  shown  in  section  in  Fig.  66,  in 


617 


52 


PLUMBING. 


which  A  is  the  gas  valve,  B  the  water  valve,  D  the  pilot  light, 
FF  the  burners,  I  a  conical  heating  ring,  J  a  disc  to  retard  and 
spread  the  rising  heat,  K  a  perforated  copper  screen,  and  L  a 
revolving  water  distributer.  In  this  heater  the  water  is  exposed 
directly  to  the  heated  air  and  gases  in  addition  to  its  passing  over 
the  heated  surface  of  the  ring  I.  The  upward  arrows  show  the 
path  of  the  heat,  and  the  downward  arrows  the  passage  of  the 
water. 


Fig.  64. 
GAS  nETERS. 

The  meter  should  be  placed  in  such  a  position  that  it  is  easily 
accessible  and  may  be  read  without  the  use  of  an  artificial  light. 
It  is  connected  into  the  system  between  the  service  pipe  and  main 
riser  to  the  building,  the  connections  being  made  as  shown  in 
Fig.  67. 

Different  meters  vary  but  little  in  the  arrangement  of  the 
dials.  In  large  meters  there  are  often  as  many  as  five  dials,  but 
those  used  for  dwelling  houses  usually  have  but  three.  Fig.  68 
shows  the  common  form  of  index  of  a  dry  meter.  The  small  index 
haml,  D,  on  the  upper  dial  is  not  taken  into  consideration  wheu 


5)8 


PLUMBING. 


53 


reading  the  meter,  but  is  used  merely  for  testing.-  The  three  dials, 
which  record  the  consumption  of  gas,  are  marked  A,  B  and  C,  and 
each  complete  revolution  of  the  index  hand  denotes  1,000,  10,000 
and  100,000  cubic  feet  respectively.  It  should  be  noted  that  the 
index  hands  on  the  three  dials  do  not  move  in  the  same  direction ; 


Fig.  65. 

A  and  C  move  with  the  hands  of  a  watch,  and  B  in  the  opposite 
direction.  The  index  shown  in  Fig.  68  should  be  read  48,700. 
Suppose  after  being  used  for  a  time,  the  hands  should  have  the 
position  shown  in  Fig.  69.  This  would  read  64,900,  and  the 
amount  of  gas  used  during  this  time  would  equal  the  difference 
in  the  readings :  64,900  —  48,700  =  16,200  cubic  feet 


019 


PLUMBING. 


GAS   HACHINES. 

While  tlie  manufacture  of  gas  for  cities  and  towns  is  a  matter 
beyond  the  scope  of  gas  fitting,  it  may  nut  be  out  of  place  to  take 
up  briefly  the  operation  of  one  of  the  forms  of  gas  machines 


Sf/f  V/Ce  PtPE 


Fig.  66. 


which  are  used  for  supplying  .private  residences  or  manufacturing 
plants. 

The  general  arrangement  of  the  apparatus  is  shown  in  Fig. 


Fig-  69. 

70,  which  consists  of  a  generator,  containing  evaporating  pans  or. 
chambers,  and  an  automatic  air  pump,  together  with  the  necessary 
piping  for  air  and  gas.  The  gas  made  by  these  machines  is  com- 


!T20 


PLUMBING. 


55 


521 


56 


PLUMBING. 


monly  known  as  carbureted  air  gas,  being  common  air  impregnated 
with  the  vapors  of  gasoline.  It  burns  with  a  rich  bright  flame 
similar  to  coal  gas,  and  is  conducted  through  pipes  and  fixtures  in 
the  same  manner. 

Referring  to  Fig.  70,  the  automatic  air  pump  is  seen  in  the 
cellar  of  the  house,  and  connected  to  it  and  running  underground 
are  the  air  and  gas  pipes  connecting  it  with  the  generator,  which 
may  be  a  hundred  feet  or  more  away  if  desired.  When  the  m*t<- 

chine  is  in  operation,  the  pump 
forces  a  current  of  air  through 
the  generator,  where  it  becomes 
carbureted,  thus  forming  an 
illuminating  gas  that  is  return- 
ed through  the  gas  pipe  to  the 
house,  where  it  is  distributed  to 
the  fixtures  in  the  usual  way. 
The  operation  is  automatic,  gas 
being  generated  only  as  fast  and 
in  such  quantities  as  required 
for  immediate  consumption. 
The  process  is  continuous  while 
the  burners  are  in  use,  but  stops 
as  soon  as  the  lights  are  extin- 
guished. Power  for  running 
the  air  compressor  is  obtained 
by  the  weight  shown  at  the 
right,  which  must  be  wound  up 
at  intervals,  depending  upon  the 
amount  of  gas  consumed.  An 
air  compressoi  to  be  run  by  wa- 
ter power  is  shown  in  Fig.  71. 

The  action  of  this  machine  is  entirely  automatic,  the  supply  of 
water  being  controlled  by  the  rising  and  falling  of  the  holder  A. 
which,  being  attached  by  a  lever  to  the  valve  B,  regulates  the 
amount  of  water  supplied  to  the  wheel  in  exact  proportion  to 
the  number  of  burners  lighted.  If  all  the  burners  are  shut  off, 
the  pressure  accumulating  in  the  holder  A  raises  it  and  shuts  the 
water  oif.  If  a  burner  is  lighted,  the  holder  falls  slightly,  allow- 


Fig.  71. 


PLUMBING. 


ing  just  enough  water  to  fall  upon  the  wheel  to  furnish  the  amount 
of  gas  required.  A  pump  or  compressor  of  this  kind  requires 
about  two  gallons  of  water  per  hour  for  each  burner.  The  advan- 


tages of  a  water  compressor  over  one  operated  by  a  weight  are 
that  it  requires  no  attention,  never  runs  down  and  is  ready  for 
immediate  use  at  all  times. 

The  generator  is  made  up  of  a  number  of  evaporating  pans  or 
chambers  placed  in  a  cylinder  one  above  another.     These  chambers 


523 


58 


PLUMBING. 


are  divided  by  supporting  frames  into  winding  passages,  which 
give  an  extended,  surface  lor  evaporation.  Fig.  72  shows  the 
generator  when  set  with  a  brick  pit  and  manhole  at  one  side.  It 
is  supplied  with  mica  gages  for  showing  the  amount  of  gasoline  in 
each  pan,  and  with  tubes  and  valves  for  distributing  it  to  the  differ- 
ent pans  as  required.  In  small  plants  the  generator  is  usually 
buried  withuiit  the  pit  being  provided,  but  for  larger  plants  the 

setting  shown  in 
Fig.  72  is  recom- 
mended. Car- 
bureted air  gas 
of  s  t  a  n  d  a  r  d 
quality  contains 
15  per  cent  of 
vapor  to  85  per 
cent  of  air.  A 
regulator  or 
mixer  for  sup- 
plying gas  hav- 
ing these  pro- 
portions is 
shown  in  section 
in  Fig.  73.  It 
consists  of  a 
cast-iron  case  in 
which  is  sus- 
pended a  sheet- 
metal  can,  B, 
filled  with  ai  r 

and  closely  sealed.  The  balance  beam  E,  to  which  this  is  hung,  is 
supported  by  the  pin  H,  on  agate  bearings.  Since  the  weight  of  the 
can  B  is  exactly  balanced  by  the  ball  on  the  beam  E,  movement  of  B 
can  only  be  caused  by  a  difference  in  the  weight  or  density  of  the 
gas  inside  the  chamber  A  and  surrounding  the  can  B.  If  the  gas 
becomes  too  dense,  B  rises  and  opens  the  valve  C,  thus  admitting 
more  air:  and  if  it  becomes  too  light,  C  closes  and  partially  or 
wholly  shuts  off  the  air,  as  may  be  required. 


Fig. 


524 


REVIEW  QUESTIONS. 


PRACTICAL  TEST  QUESTIONS. 

In  the  foregoing  sections  of  this  Cyclopedia 
numerous  illustrative  examples  are  worked  out  in 
detail  in  order  to  show  the  application  of  the  various 
methods  and  principles.  Accompanying  these  are 
examples  for  practice  which  will  aid  the  reader  in 
fixing  the  principles  in  mind. 

In  the  following  pages  are  given  a  large  number 
of  test  questions  and  problems  which  afford  a  valu- 
able means  of  testing  the  reader's  knowledge  of  the 
subjects  treated.  They  will  be  found  excellent  prac- 
tice for  those  preparing  for  College,  Civil  Service,  or 
Engineer's  License.  In  some  cases  numerical  answers 
are  given  as  a  further  aid  in  this  work. 


525 


REVIEW    QUESTIONS 

ON     THE     SUBJECT     OF1 

MACHINE    DESIGN. 

PART    I'. 


The  drawings  made  in  accordance  with  the  problems  below 
should  be  traced  in  ink  on  tracing  cloth  18  by  24  inches  in  size, 
and  having  a  border  line  ^  inch  inside  the  edge  of  the  paper. 

PROBLEMS. 

1.  Suppose  a  30-inch,  pulley  is  substituted  for  the  42-inch 
in  the  problem  given,  and  that  the  pulley  on  the  motor  remains 
10A  inches  as  before,  how  fast  must  the  motor  run  to  give  the  rope 
the  same  speed,  150  feet  per  minute  ? 

2.  Will  the  horse -power  of  the  motor  be  changed  with  this 
new  condition  ?     Explain  fully. 

3.  Calculate  the  width  of  double  belt  for  above  condition. 

4.  What  is  the  torque  on  the  motor  shaft  for  above  condition? 

5.  Calculate  the  size  of  shaft  in  the  small  pulley  for  above 
condition. 

6.  Calculate  the  size  of  shaft  in  the  30- inch  pulley  for  above 
condition. 

7.  Design  and  draw  both  pulleys  for  above  condition,  mak- 
ing complete  working  drawings,  and  giving  all  calculations  in  full. 

8.  Taking  the  original  problem  as  given  in  the  text,  suppose 
it  is  desired  to  increase  the  large  gear  to  45  inches  diameter,  cal- 
culate the  load  on  the  tooth,  and  a  suitable  pitch  and  face  to  take 
this  load. 

9.  How  many  teeth  must  the  pinion  have  to  give  the  same 
speed  of   rope,    150    feet  per  minute,  assuming  that  the  motor 
runs  470  revolutions  per  minute,  for  condition  in  Problem  8  ? 

10.  Calculate  the  bore  of  pinion  for  this  case. 

11.  Design  and  draw  the  gears  for  the  conditions  of  Prob- 
lems 8  and  9,  giving  all  calculations  in  full.         '    . 


MACHINE  DESIGN 


12.  When  there  is  but  3.000  pounds  on  the  rope,  what  are 
the  tensions  in  each  end  of  the  brake  strap,  assuming  that  the  size 
of  drum  and  other  conditions  remain  the  same  ? 

13.  llo\v  much  pressure  on  the  foot  lever  would  it  take  to 
hold  this  load  of  3.000  pounds  on  the  rope  ? 

11.  Suppose  we  put  a  bearing  9  inches  long  on  the  drum 
shaft;  the  distance,  center  to  center  of  bearings,  would  then  be  3 
feet  5|  inches,  gears,  drum,  brake,  and  load  being  same  a.?  in  the 
original  problem  of  the  text.  Calculate  the  diameter  of  the  drum 
shaft. 

15.  Suppose  the  height  of  bracket,  center  to  base,  to  be  15 
inches;  length  and  diameter  of  bearing,  as  in  Problem  14;  and  that 
we  use  a  separate  bracket  for  the  drum  bearings,  not  connected 
with  the  pinion -shaft  bearings.  Design  and  draw  such  a  bracket. 

10.  Calculate,  design,  and  draw  all  the  parts  for  a  machine 
similar  to  that  of  the  text,  from  the  following  data: 

Load  on  rope 4.000  pounds. 

Speed  of  rope 175  feet  per  minute. 

Length  of  rope  to  be  reeled  in  ....  250  feet. 

NOTE.  Problems  12,  13  and  15  are  comparatively  simple,  following 
closely  the  steps  of  the  text  in  their  solution. 

Problem  16,  likewise,  is  supposed  to  be  worked  out  on  the  same  lines  as 
the  text,  but  is  wholly  original  in  its  nature,  being  based  on  entirely  new  data. 
It  is  not  expected  that  this  problem  will  be  attempted  except  by  well-advanced 
students  who  can  give  considerable  time  to  working  it  out  completely.  It  will 
be  found,  however,  an  excellent  exercise  in  original  and  yet  simple  design. 


REVIEW    QUESTIONS 


U  11  .1  E  C  T      OF1 


HEATIXG    AXD  VEXTILATIOX 


A.  K  T     I  . 


1.  What  advantage  does  indirect  steam  heating  have  over 
direct  heating?    What  advantages  over  furnace  heating? 

2.  What  are  the  causes  of  heat  loss  from  a  building? 

3.  Why  is  hot  water  especially  adapted  to  the  warming  of 
dwellings? 

4.  What  proportion  of  carbonic  acid  gas  is  found  in  outdoor  air 
under  ordinary  conditions? 

5.  A  room  in  the  N.  E.  corner  of  a  building  of  fairly  good  con- 
struction is  18  feet  square  and  10  feet  high ;  there  are  5  single  windows 
each  3  by  10  feet  in  size.     The  walls  are  of  brick  12  inches  in  thickness. 
With  an  inside  temperature  of  70  degrees,  what  will  be  the  heat  loss 
per  hour  in  zero  weather? 

C.  State  four  important  points  to  be  noted  in  the  care  of  a  fur- 
nace. 

7.  A  grammar  school  building,  constructed  in  the  most  thor- 
ough manner,  has  4  rooms,  one  in  each  corner,  each  being  30  ft.  by 
30  ft.  and  14  ft.  high,  and  seating  50  pupils.  The  walls  are  of  wooden 
construction,  and  the  windows  make  up  -3  of  the  total  exposed  surface. 
The  basement  and  attic  are  warm.  How  many  pounds  of  coal  will  be 
required  per  hour  for  both  heating  and  ventilation  in  zero  weather,  if 
8,000  B.  T.  U.  are  utilized  from  each  pound  of  coal? 

S.  What  two  distinct  types  of  furnaces  are  used?  What  are 
the  distinguishing  features? 

9.  What  is  meant  by  the  efficiency  of  a  furnace?  What  effi- 
ciencies are  obtained  in  ordinary  practice? 


529 


HEATING  AND   VENTILATION 


10.  What  are  the  principal  parts  of  a  furnace?     State  briefly 
the  use  of  each. 

11.  A  brick  house  of  the  best  construction,  20  ft.  by  40  ft.,  has 
3  stories,  each  10  feet  high.     The  walls  are  12  inches  in  thickness; 
and  3  the  total  exposed  wall  is  taken  up  by  windows,  which  are  double. 
The  basement  is  warm,  but  the  attic  is  cold.     The  house  is  to  be 
warmed  to  70  degrees  when  it  is  ten  degrees  below  zero  outside.     How 
many  square  feet  of  grate  surface  will  be  required,  assuming  usual 
efficiencies  of  coal  and  furnace? 

12.  A  high  school  is  to  be  provided  with  tubular  boilers.     What 
H.  P.  will  be  required  for  warming  and  ventilation  in  zero  weather  if 
there  are  GOO  occupants,  and  the  heat  loss  through  walls  and  windows 
is  1,500,000  B.  T.  V.  per  hour? 

13.  What  are  the  three  essential  parts  of  any  heating  system? 

14.  Is  direct-steam  heating  adapted  to  the  warming  of  school- 
houses  and  hospitals?     (rive  the  reason  for  your  answer. 

15.  The  heat  loss  from  a  dwelling-house  is  280,000  B.  T.  U.  per 
hour.     It  is  to  be  heated  with  direct  steam  by  a  type  of  sectional  boiler 
in  which  the  ratio  of  heating-  surface  to  grate  surface  is  28.     What  will 
be  the  most  efficient  rate  of  combustion,  and  how  many  square  feet  of 
grate  surface  will  be  required? 

10.     What  is  the  use  of  a  blow-off  tank?     Show  by  a  sketch  how 
the  connections  are  made. 

17.  How  are  the  sizes  of  single-pipe  risers  computed? 

18.  What  weight  of  steam  will  be  discharged  per  hour  through 
a  6-inch  pipe  300  feet  long,  with  an  initial  pressure  of  10  pounds,  and  a 
drop  of  f  pound  in  its  entire  length? 

10.     What  is  an  air-valve?     Upon  what  principles  does  it  work? 

20.  What  size  of  steam  pipe  will  be  required  to  discharge  2,400 
pounds  of  steam  per  hour  a  distance  of  900  feet,  with  an  initial  pres- 
sure of  GO  pounds,  and  a  drop  in  pressure  of  5  pounds? 

21.  What  objection  is  there  to  a  single-pipe  riser  system?     How 
is  this  sometimes  overcome  in  large  buildings? 

22.  What  patterns  of  valves   should   be   used    for  radiators? 
What  conditions  of  construction  must  be  observed  in  making  the  con- 
nections betweeii  the  radiator  and  riser? 


530 


REVIEW     QUESTIONS 


ON     THE     SUBJECT     OF1 


HEATING    AND  VENTILATION 


PART     II. 


1.  How  would  you  obtain  the  sizes  of  the  cold-air  and  warm- 
air  pipes  connecting  with  indirect  heaters  in  dwelling-house  work? 

2.  What  is  an 'aspirating  coil,  and  what  is  its  use? 

3.  What  efficiencies  may  be  allowed  for  indirect  heaters  in 
schoolhouse  work?     How  would  you  compute  the  size  of  an  indirect 
heater  for  a  room  in  a  dwelling-house? 

4.  How  is  the  size  of  a  direct-indirect  radiator  computed? 

5.  A  schoolroom  on  the  third  floor  is  to  be  supplied  with  2,400 
cubic  feet  of  air  per  minute.     What  should  be  the  area  of  the  warm- 
air  supply  flue? 

0.     What  is  the  chief  objection  to  a  mixing  damper,  and  how 
may  this  be  overcome? 

7.  How  many  square  feet  of  indirect  radiation  will  be  required 
to  warm  and  ventilate  a  schoolroom  when  it  is  10  degrees  below  zero, 
if  the  heat  loss  through  walls  and  windows  is  42,000  B.  T.  U.,  and  the 
air-supply  120,000  cubic  feet  per  hour? 

8.  What  is  the  difference  in  construction  oetween  a  steam 
radiator  and  one  designed  for  hot  water?     Can  the  steam  radiator 
be  used  for  hot  water?     State  reasons  for  answer. 

9.  How  may  the  piping  in  a  hot-water  system  be  arranged  so 
that  no  air-valves  will  be  required  on  the  radiators? 

10.  What,  efficiency  is  commonly  obtained  from  a  direct  hot- 
water  radiator?     How  is  this  computed? 

11.  How  should  the  pipes  be  graded  in  making  the  connections 
with  indirect  hot-water  heaters?    Where  should  the  air-valve  be 
placed? 


531 


HEATING  AND  VENTILATION 


12.  Describe  briefly  one  form  of  grease  extractor. 

13.  What  is  the  office  of  a  pressure-reducing  valve  in  an  exhaust- 
steam  heating  system? 

14.  Upon  what  principle  does  a  pump  governor  operate? 

15.  "What  type  of  pipe  fittings  should  always  be  used  in  hot- 
water  work? 

10.  How  is  the  water  of  condensation  returned  to  the  boilers 
in  exhaust  steam  heating? 

17.  How  many  cubic  feet  of  air  per  hour  will  be  discharged 
through  a  flue  2  feet  by  3  feet,  and  00  feet  high,  if  the  air  in  the  flue 
has  a  temperature  of  SO  degrees  and  the  outside  air  GO  degrees? 

IS.  In  a  hot-water  heating  system,  what  causes  the  water  to  flow 
through  the  pipes  and  radiators?  How  does  the  height  of  the  radiator 
above  the  boiler  affect  the  flow? 

10.  What  precaution  should  always  be  taken  before  starting 
a  fire  under  a  steam  boiler? 

20.  What  is  the  free  opening  in  square  feet  through  a  register  24 
inches  by  4S  inches? 

21.  Why  are  return  pumps  or  return  traps  necessarv  in  exhaust- 
steam  heating  plants? 

22.  What  efficiency  may  be  obtained  from  indirect  hot-water 
radiators  under  usual  conditions?     What  is  the  common  method  of 
computing  indirect  hot-water  surface  for  dwelling-house  work? 

23.  State  briefly  how  a  return  trap  operates. 

24.  What  is  the  use  of  an  'expansion  tank,  and  what  should  be 
its  capacity? 

25.  Describe  the  action  of  one  form  of  damper  regulator. 

20.  What  is  the  principal  difference  between  a  hot-water  heater 
and  a  steam  boiler?  What  type  of  heater  is  best  adapted  to  the 
warming  of  dwelling-houses? 

27.  Upon  what  four  conditions  does  the  size  of  a  pipe  to  supply 
any  given  radiator  depend? 

28.  What  is  the  use  of  an  exhaust  head? 

20.  A  hospital  ward  requires  00,000  cubic  feet  of  air  per  hour 
for  ventilation,  and  the  heat  loss  through  walls  and  windows  is  140,000 
B.  T.  U,  per  hour.  How  many  square  feet  of  indirect  steam  radiation 
will  be  required  in  zero  weather? 

30.     For  what  purpose  is  a  back-pressure  valve  used? 


532 


REVIEW     QUESTIONS 

OX      THE      SUBJECT      OF 

HEATING    AND  VENTILATION. 

PART    III 


1.  A  main  heater  contains  1,040  square  feet  of  heating  surface 
made  up  of  wrought-iron  pipe,  and  is  used  in  connection  with  a  fan 
which  delivers  528,000  cubic  feet  of  air  per  hour.     The  heater  is  20 
pipes  deep,  and  has  a  free  area,  between  the  pipes,  of  11  square  feet. 
If  air  is  taken  at  zero,  to  what  temperature  will  it  be  raised  with  steam 
at  5  pounds'  pressure. 

2.  An  8-foot  fan  used  for  schoolhouse  ventilation  runs  at  a 
speed  of  124  r.  p.  m.     What  horse-power  of  engine  is  required?    What 
horse-power  would  be  required  if  the  fan  were  speeded  up  to  134.6 
r.  p.  m.? 

3.  What  precaution  must  be  taken  in  connecting  the  radiators 
in  tall  buildings? 

4.  Give  the  size  of  heater  from  Table  XXXI  which  will  be 
required  to  raise  672,000  cubic  feet  of  air  per  hour,  from  10°  below 
zero  to  95°,  with  a  steam  pressure  of  20  pounds.     If  the  air-quantity 
is  raised  to  840,000  cubic  feet  per  hour  through  the  same  heater,  what 
will  be  the  resulting  temperature  with  all  other  conditions  the  same? 

5.  A  fan  running  at  150  revolutions  produces  a  pressure  of  ^ 
ounce.     If  the  speed  is  increased  to  210  revolutions,  what  will  be  the 
resulting  pressure? 

6.  A  certain  fan  is  delivering  12,000  cubic  feet  of  air  per  minute, 
at  a  speed  of  200  revolutions.     It  is  desired  to  increase  the  amount  to 
18,000  cubic  feet.     What  will  be  the  required  speed?     If  the  original 
power  required  to  run  the  fan  was  4  H.  P.,  what  will  be  the  final  power 
due  to  the  increased  speed? 

7.  What  size  fan  will  be  required  to  supply  a  schoolhouse 


533 


HEATING  AND  VENTILATION 


having  300  pupils,  if  each  is  to  be  provided  with  3,000  cubic  feet  of 
air  per  hour?  What  speed  of  fan  will  be  required,  and  what  H.  P.  of 
engine? 

8.  What  advantages  has  the  plenum  method  of  ventilation  over 
the  exhaust  method? 

9.  A  church  is  to  be  warmed  and  ventilated  by  means  of  a  fan 
and  heater.     The  air-supply  is  to  be  300,000  cubic  feet  per  hour. 
The  heat  loss  through  walls  and  windows  is  200,000  B.  T.  U.,  when  it 
is  zero.     How  many  square  feet  of  heating  surface  will  be  required, 
and  how  many  rows  of  pipe  deep  must  the  heater  be,  with  steam  at  5 
pounds'  pressure? 

10.  A  schoolhouse  requiring  600,000  cubic  feet  of  air  per  hour 
is  to  be  supplied  with  a  cast-iron  sectional  heater  of  the  pin  type.     How 
many  square  feet  of  radiating  surface  will  be  required  to  raise  the  air 
from  10°  below  zero  to  70°  above,  with  a  steam  pressure  of  10  pounds? 

11.  What  velocities  of  air-flow  in  the  main  duct  and  branches 
are  commonly  used  in  connection  with  a  fan  system? 

1 2.  A  main  heater  is  to  be  designed  for  use  in  connection  with 
a  fan.     How  many  square  feet  of  radiation  will  be  required  to  warm 
1,000,000  cubic  feet  of  air  per  hour,  from  a  temperature  of  10°  below 
zero  to  70°  above,  with  a  steam  pressure  of  5  pounds  and  a  velocity 
of  800  feet  per  minute  between  the  pipes  of  the  heater?     How  many 
rows  of  pipe  deep  must  the  heater  be? 

13.  State  in  a  brief  manner  the  essential  parts  of  a  system  of 
automatic  temperature  control. 

14.  What  advantage  does  an  indirect  steam-heating  system  have 
over  furnace  heating  in  schoolhouse  work? 

15.  The  air  in  a  restaurant  kitchen  is  to  be  changed  every  10 
minutes  by  means  of  a  disc  fan.     The  room  is  60  by  30  by  10  feet. 
Give  size  and  speed  of  fan,  and  H.  P.  of  motor. 

16.  What  forms  of  heating  are  best  adapted  to  the  warming  of 
apartment  houses? 

17.  Give  an  approximate  method  for  finding  the  heating  surface 
required  for  greenhouses,  both  for  steam  and  hot  water. 

18  How  does  the  cost  of  electric  heating  compare  with  that  by 
steam  and  hot  water? 

19.  Describe  briefly  the  construction  of  an  electric  heater,  and 
the  principle  upon  which  it  works. 


534 


HEATING  AND  VENTILATION 


20.  A  school  building  of  4  rooms  is  to  be  supplied  with  600,000 
cubic  feet  of  air  per  hour.     The  heat  loss  from  the  building  is  300,000 
B.  T.  U.  per  hour  in  zero  weather.      Give  the  square  feet  of  grate  sur- 
face required  in  the  furnaces. 

21.  What  is  a  double-duct  system  as  applied  to  forced-blast 
heating?     What  are  its  advantages? 

22.  What  is  a  thermostat?     Give  the  principles  upon  which  two 
different  kinds  operate. 

23.  Describe  briefly  the  connections  to  be  made  in  a  system 
of  electric  heating.     In  what  way  do  they  correspond  to  the  piping 
in  a  system  of  steam  heating? 

24.  State  certain  points  to  be  observed  in  the  introduction  of 
air  for  the  ventilation  of  churches'and  theaters. 

25.  A  shop  100  feet  long,  50  feet  wide,  and  having  5  stories, 
each  10  feet  high,  is  to  be  warmed  by  forced  blast  using  steam  at  80 
pounds'  pressure.     The  full  amount  of  air  passed  through  the  heater 
is  to  be  taken  from  out  of  doors,  and  the  entire  air  of  the  building 
changed  3  times  an  hour.     Give  linear  feet  of  1-inch  pipe  required 
for  heater,  and  size  of  fan  and  engine. 

26.  In  what  cases  would  you  use  a  disc  fan  in  preference  to  a 
blower? 

27.  The  heat  loss  from  a  room  is  12,000  B.  T.  U.  per  hour. 
How  many  kilowatt-hours  will  be  required  to  furnish  the  necessary 
heat? 

28.  What  is  one  of  the  best  systems  for  the  heating  and  venti- 
lation of  school  buildings  of  large  size? 

29.  What  form  of  heating  system  would  you  recommend  for  a 
four-room  school? 

30.  A  factory  250  feet  long  by  50  feet  wide  has  two  stories,  each 
10  feet  high.     Each  floor  is  to  have  a  separate  fan  and  heater,  but  the 
fans  are  to  be  driven  by  the  same  electric  motor.     The  lower  floor  is 
to  be  supplied  with  air  from  out  of  doors,  and  is  to  have  a  complete 
change  of  air  every  20  minutes.     On  the  upper  floor  the  air  is  to  be 
returned  to  the  heater  from  the  room,  and  the  entire  contents  is  to 
pass  through  the  heater  every  20  minutes.     Exhaust  steam  is  to  be 
used  in  both  heaters.     Give  sizes  of  fans,  heaters,  and  motor. 

31.  What  is  a  telethermometer? 

32.  Describe  two  methods  of  moistening  air. 


635 


\r  I  K  W     Q  UK  S  T  I  O  X  S 


PLUMUIXCi. 

PART    I. 


1.  What  causes  a  trap  to  ". siphon.''  and  in  what  three  ways 
may  it  be  prevented? 

2.  What  size  of  soil  pipe  should  be  used  for  an  ordinary- 
sized  dwelling,  and  what  pitch  should   bo  given   to  the  horizontal 
portion  ? 

3.  What  quantity  of  water  per  capita  should  be  allowed  in 
designing  a  sewerage  system? 

4.  What  form  of  cross-section  of  conduit  gives  a  maximum 
velocity  of  flow  to  smrJl  quantities  of  sewage? 

o.  Describe  the  manner  of  making  house  connections  with 
the  m;iin  sewer. 

!).  Show  by  sketch  the  general  method  of  running  the 
waste  and  ye:it  pipes  in  a  dwelling  house,  and  indicate  the  proper 
location  of  traps. 

T.  What  are  the  two  principal  methods  of  sewage  purifi- 
cation ? 

8.  Describe   the  method  of  making  up  the  joints  in  cast 
iron  soil  pipe. 

9.  In  what  way  may  the  seal  of  a  trap  be   broken  besides 
siphonage? 

10.     What  two  tests  are  usually  given  to  a  .system  of  plumb- 
iiiir'/     State  the  use  of  each. 


536 


PLUMBING. 


11.  What   grade    should    be    given    to    main   sewers   and 
branches  ? 

12.  Give  two  methods  of  flushing  sewers. 

13.  Describe  briefly  some  of  the  usual  arrangements  in  the 
plumbing  of  hotels. 

14.  What  is  sewage  farming  ?     Describe  the  process  briefly. 

15.  What  is  the  difference  between  a  "cup  joint"  and  a 
44  wipe  joint?"     State  the  conditions  under  which  you  would  use 
each. 

16.  What  is  the  use  of  a  fresh-air  inlet  in  connection  with 
a  soil  pipe,  and  how  is  it  connected  ? 

17.  Describe  the  "  Smoke  Test." 

18.  Should  a  trap  or  fixture    be  vented  into  a  chimney  ? 
Give  the  reasons  for  your  answer. 

1 9.  What  material   is  commonly  used  for  sewer  pipes  of 
different  sizes  ? 

20.  When  are  underdrains  required  and  how  are  they  con- 
structed ? 

21.  What    precautions  should    be    taken    in    back   venting 
traps  ? 

22.  What  chemicals  are  commonly  used  in  the  precipitation 
of  sewage  ? 

23.  How  should  you  connect   a   lead  pipe  with  a  cast  or 
wrought  iron  pipe? 

24.  Define    the    "  separate "    and    "  combined "  systems    of 
sewerage. 

25.  What  is  the  principal  point  to  be  observed  in  the  dis- 
posal of  sewage  ?     What  precautions  should  be  taken  when  it  is 
discharged  into  a  stream  ? 

26.  What  is  the  sedimentation  process  ? 

27.  What   precautions  should  be  taken  in  locating  a  cess- 
pool?    Describe  briefly  one  form  of  construction. 

28.  Name  some  of  the  most  important  data  to  be  obtained 
before  laying  out  a  system  of  sewerage. 

29.  In  designing  a  system  of  surface  drains  what  maximum 
conditions  should  be   provided  for? 

30.  Under  what  conditions   may  sub-surface    irrigation  be 
used  to  advantage? 


537 


R  K  V  I K  W    Q  U  K  S  T I  O  N"  S 

O  V     T  IT  l-i     !ST*  J5.T  KC"T    O  1* 

PLUMBING. 

PART     II. 


1.  A  hotel  requires  a  water  supply  of  200  gallons  of  water 
per    minute  during'  a  certain  part  of    the  day.      It  receives  its 
supply  from  a  reservoir  1,000  feet  distant,  and  located  116  feet 
above  the  house  tank,  in  the  attic  of  the  building.      What  size  of 
wrought-iron  pipe  will   be  required  to   bring  the  water  from  the 
reservoir  ? 

Ans.  3  inch. 

2.  What  is  the  best  kind  of  pipe  for  domestic  water  supply 
under  ordinary  conditions?      When  may  it  be  objectionable? 

3.  A  1-inch  pipe  is  to  discharge   40  gallons  of  water  per 
minute  from  a  cistern  placed  directly  above  it.     What  must  be 
the  elevation  if  we  assume  the  friction  in  the  pipe  and  bends  to 
be  equivalent  to  100  feet? 

Ans.  Ill  feet. 

4.  A  house  tank  is  situated  15  feet  above  a  faucet  upon 
the  fifth  floor  of  the  building.      If  the  stories  are  8  feet  high,  what 
will    be   the   difference   in    pressure  in  pounds  per  square   inch 
between  this  faucet  and  one  in  the  basement? 

Ans.  17.3  pounds. 

5.  Describe  the  action  of  an  hydraulic  ram. 

6.  A  pump  has   a  steam  cylinder  6  inches  in  diameter  and 
a  watet- cylinder  5  inches  in  diameter.     What  steam  pressure  will 
be  required  to  raise  water  to  an  elevation  of  135  feet,  neglecting 
friction  in  the  pipe  ? 

Ans.  40.3  pounds. 


538 


INDEX 


The  page  numbers  of  this  volume  will  be  found  at  the  bottom  of  the 
pages;  the  numbers  at  the  top  refer  only  to  the  section. 


Page 

Page 

A 

Blow-oil  tank 

264 

Air 

Boiler  connections 

263 

analysis  of 

204 

Bolts 

163 

force  for  moving 

207 

Brackets 

59,  184 

required  for  ventilation 

205 

Brass  pipe 

432,  476 

velocity  of 

207 

British  thermal  unit 

209 

Air-compressor 

385 

Broad  irrigation 

465 

Air  distribution 

208 

Bunsen  burner 

509 

Air-filters 

390 

Burners 

Air-leakage 

210 

argand 

508 

Air-  valves 

254,  305 

bat's  wing 

508 

Air-  vent  ing 

301 

Bunsen 

509 

Air-washers 

390 

fish-tail 

508 

Argand  burner 

508 

single-  jet 

507 

Atmosphere,  composition  of 

203 

C 

Automatic  return-pumps 

326 

Cap  screws 

172 

B 

Carbonic  acid  gas 

203 

Back-pressure  valve 

324 

Cast-iron  pipe 

429 

Back  venting 

439 

Catch-basins 

461 

Balance-pipe 

327 

Centrifugal  fan 

355,  359 

Bath  room  pipe  connections 

443 

Centrifugal  pumps 

316 

Bath  tubs 

411 

Centrifugal  whirling 

123 

Bat's-  wing  burner 

'      508 

Cesspools 

435 

Beams 

24 

Chemical  precipitation 

463 

Bearings 

184 

Chimney  flues 

224 

Belting 

Circulation  coils 

241 

horse-power  transmitted  by 

95 

Cisterns  and  tanks 

479 

material  of 

97 

Clamp  coupling 

162 

speed  of 

97 

Claw  coupling 

162 

Belts 

89 

Cold-air  box 

224 

initial  tension  in 

98 

Cold-air  ducts 

278 

problems  on 

99 

Cold-water  supply 

480 

Bessemer  steel 

127 

Combined  stresses 

117 

Bevel  gears 

140 

Combustion  chamber. 

220 

Blast  area 

361 

Compression 

25 

Note.  —  For  page  numbers  see  foot  of  p 

•ages. 

539 


11 


IXDEX 


Page 

Page 

Cone  fans 

356 

Design 

Constructive  mechanics 

24 

stands 

184 

Cotters 

180 

studs 

163 

Couplings 

159 

tabulation  of  torsional  moments 

43 

theoretical 

20 

D 

worm  gears 

146 

Damper-regulators 

330 

Diaphragm  motors 

388 

Dampers                                                     273, 

388 

Diaphragm  valve 

387 

Deflection  of  shaft 

121 

Direct  hot-water  heating 

200,  293 

Design 

18 

air-venting 

301 

application  of 

35 

efficiency  of  radiators 

296 

base  of  machine 

69 

expansion  tank 

299 

bearings 

184 

overhead  distribution 

299 

belt  width 

43 

pipe  connections 

301 

belts 

89 

piping 

297 

bevel  gears 

140 

radiating  surface 

295 

bolts 

163 

systems  of  circulation 

294 

brackets 

184 

valves  and  fittings 

305 

brackets  and  caps 

59 

Direct-indirect  radiators 

200,  2S7 

brake-relief  spring 

69 

Direct  -steam  heating 

198,  238 

conditions  and  forces 

18 

cast-iron  radiators 

239 

cotters 

180 

circulation  coils 

241 

couplings 

159 

pipe  radiators 

241 

data  on  sketch 

44 

piping  systems 

245 

delineation 

22 

Disc  fans 

355,  367 

driving  gears 

38 

capacity  of 

368 

drum  and  brake 

63 

Domestic  water  supply 

469 

foot  lever 

69 

Driving  gears 

38 

friction  clutches 

153 

Drum  and  brake 

63 

gear  guard 

69 

Drum  shaft 

49 

gears 

55 

general  drawing 

70 

E 

height  of  centers 

44 

Efficiency 

keys  and  pins 

174 

of  cast-iron  heaters 

353 

length  of  tarings 

44 

of  furnace  heating 

221 

original 

82 

of  indirect  heaters 

270 

pinion  bore 

49 

of  pipe  heaters 

348 

practical  modification 

21 

of  radiators 

243,  296 

preliminary  layout 

51 

Electric  heat  and  energy 

382 

preliminary  sketch 

38 

Electric  heating 

202,  382 

pulley  bores 

47 

Electric  motors 

373 

pulleys                                          41,  53, 

100 

Exhaust  head 

326 

rope  and  drum 

38 

Exhaust  method  of  forced  blast 

343 

shaft  diameters 

44 

Exhaust  steam  heating 

201,  320 

shafts                                                  49, 

114 

automatic  return-pumps 

326 

specification 

22 

back-pressure  valve 

324 

spur  gears 

128 

damper-regulators 

330 

Note.  —  For  page  numbers  see  foot  of  pages. 

540 


INDEX 

Page 

Exhaust  steam  heating 

Furnace  heating 

exhaust  head 

326 

radiator 

grease  extractor 

323 

Furnaces 

pipe  connections 

331 

care  and  management  of 

reducing  valves 

322 

chimney  flues 

return  traps 

328 

cold-air  box 

Expansion  of  pipes 

252 

location  of 

Expansion  tank 

299 

registers 

return  duct 

F 

smoke-pipes  of 

warm-air  pipes 

Factory  heating 

375 

Fan  engines 

371 

G 

Fans 

355 

Gas 

area  of  ducts  and  flues 

374 

cooking  by 

blast  area 

361 

heating  by 

capacity 

363 

Gas  fitting                                • 

effect  of  resistance 

364,  366 

Gas  fixtures 

power  required 

365 

brackets 

pressure 

361 

*~ 

speed 

362 

chandeliers 

Faucets 

428 

cocks 

Firepot 

219 

globes 

Fish-tail  burner 

508 

shades 

Flange  coupling 

160 

Gas  machines 

Force  for  moving  air 

207 

Gas  meter 

Forced  blast 

202,  343 

Gas  pipes 

efficiency  of  pipe  heaters 
exhaust  method 

348 
343 

testing 
Gate-valves 

form  of  heating  surface 

344 

Gears 

plenum  method 

344 

Globe  valve 

Forced  hot-water  circulation 

313 

Grates 

pumps  for 

316 

Grease  extractor 

Forces 

24 

H 

Fresh  air  inlets 

441 

Heat  loss  from  buildings 

Friction 

27 

by  air-leakage 

Friction  clutches 

153 

by  ventilation 

problems  on 

159 

through  walls  and  windows 

Furnace  heating 

215 

Heating,  boilers  used  for 

combination  systems 

229 

Heating  of 

combustion  chamber 

220 

apartment  houses 

efficiency 

221 

churches 

flrepot 

219 

conservatories 

furnaces 

216 

greenhouses 

grates 

218 

halls 

heating  capacity 

222 

hospitals 

heating  surface 

221 

office  buildings 

Note.  —  For  page  numbers  see  foot  of  pages. 

III 

Page 

220 
197 
230 
224 
224 
223 
229 
225 
223 
226 


613 

514 
500 
506 
511 
506 
511 
510 
512 
512 
520 

500,  518 
501 
505 
305 
55 
254 
218 
323 

209 
210 
214 
209 
232 

405 
400 
405 
405 
402 
398 
403 


541 


IV 

INDEX 

Page 

Heating  of 

OQO 

Lavatories 
Lead,  definition  of 

school  buildings 

40— 

Lead  pipe 

theaters 
Heating  and  ventilation 
Heating  capacity  of  furnace 

197-409 

Leather  belting 
strength  of 
table 

Heating  surfaces 

197 

Local  vents 

Heating  systems 

°00 

Lock  nuts 

direct  hot  water 
direct-indirect  radiators 

200 

Lubrication 

direct  steam 

198.  238 

M 

electric 

202 

Machine  design 

exhaust  steam 

201 

calculations 

forced  blast 

202 

definition  of 

furnaces 

197 

empirical  data 

indirect  hot-water 

201 

handbooks  in 

indirect  steam 

199 

production  of 

stoves 

197 

theory  of 

vacuum 

337 

Machine  screws 

Hook-tooth  gear 

138 

Machine  tools 

Horse-power  of  shafting 

124 

Machinery 

Horse-power  transmitted  by  telling 

95 

classification  of 

Horse-power  for  ventilation 

238 

mill  and  plant 

Hot-water  heaters 

290,  515 

motive-power 

Hot-water  supply 

485 

structural 

circulation  pipes 

491 

Manholes 

double  boiler  connections 

490 

Mechanical  straining  of  sewage 

double  water-back  connections 

490 

Mill  and  plant  machinery 

pipe  connections 

492 

Moments 

Humidostat 

389 

Mortise  teeth 

Hydraulic  ram 

478 

Motive-power  machinery 

Hydraulics  of  plumbing 

469 

Motors,  electric 

1 

Muff  coupling 

Indirect  hot-water  heating 

201,  309 

N 

Indirect  radiators 

268 

Nickel  steel 

Indirect  steam  heating 

199.  207 

Nitrogen 

direct-indirect  radiators 

287 

Nuts 

heaters  for 

268 

pipe  connection? 

285 
283 

(  )ne-pipe  circuit  system 

registers 
Intermittent  filtration 

465 
15 

One-pipe  relief  system 
Open-hearth  steel 

Invention 

Original  design 

K 

Oxygen 

Keys  and  pins 

174 

P 

L 

Paul  vacuum  system  of  heating 

Laundry  boilers 

493 

Pinion  bore 

\otc.-For  pane  numbers  sec  font  of 

pages. 

Page 

418 

148 

433,  474 

95 
98 
440 
171 
27 


11 
15 
15 
14 
13 
173 
75 

74 
81 
77 
78 
459 
463 
81 
24 
137 
77 
373 
161 


127 
203 
163 

250 

248 
127 
82 


341 
49 


542 


INDEX 


Page 

Page 

Pipe  connections 

443 

Pulley  rim 

101 

kitchen  sink 

445 

Pulleys 

41,  53,  100 

soil  and  waste  pipes 

445 

problems  on 

113 

urinal 

445 

special  forms  of 

112 

Pipe  radiators 

241 

Pumping  stations 

462 

Pipes 

Pumps 

477 

brass 

432,  476 

cast-iron 

429 

R 

expansion  of 

252 

Radiator  connections 

251 

lead 

433.  474 

Radiators 

220,  239 

tile 

434 

efficiency  of 

243 

wrought  iron 

432 

Reducing  valves 

322 

Piping 

473 

Registers 

229,  283 

Pitch,  definition  of 

148 

Return  duct 

225 

Pitch  cylinders 

130 

Return  pipes 

262 

Plenum  method  of  forced  blast 

344 

Return  traps 

328. 

Plumbing 

411-524 

Rope  and  drum 

38 

design  and  construction 

458 

catch-basin 

461 

S 

house  connections 

460 

Screws 

163 

manholes 

459 

Sectional  boilers 

235 

pumping  stations 

462 

Sedimentation 

463 

sewers 

459 

Service  pipe  connections 

483 

storm  overflows 

462 

Set  screws 

172 

tidal  chambers 

462 

Sewage,  disposal  of 

443 

underdrains 

459 

Sewage  purification 

454,  462 

Plumbing  for 

broad  irrigation 

465 

apartment  houses 

449 

chemical  precipitation 

463 

dwelling  houses 

449 

intermittent  filtration 

465 

factories 

452 

mechanical  straining 

463 

railroad  stations 

451 

sedimentation 

463 

schoolhouses 

451 

sub-surface  irrigation 

465 

shops 

452 

Sewerage 

454 

Plumbing  fixtures 

411 

Sewers 

459 

bath  tubs 

411 

Shafts 

114 

faucets 

428 

centrifugal  whirling 

123 

lavatories 

418 

combined  stresses 

117 

sinks 

419 

deflection 

121 

tanks 

424 

horse-power  of 

124 

traps 

422 

material  used  in 

127 

urinals 

416 

problem  on 

128 

water  closets 

412 

simple  bending 

117 

Plumbing  tests 

452 

simple  torsion 

117 

Propeller  fans 

367 

tension 

118 

Pulley  arms 

103 

Shrouding  a  tooth 

137 

Pulley  bores 

47 

Simple  bending 

117 

Pulley  hub 

105 

Simple  torsion 

117 

Note.  —  For  page  numbers  see  foot  of 

pages. 

043 


VI 


INDEX 


Single-jet  burner 

Sinks 

Siphonage 

Smoke-pipes 

Soil  pipe  vent 

Soil  and  waste  pipes 

brass 

cast-iron 

lead 

pipe  joints 

tile 

wrought  iron 
Spline 

Split  pulleys 

Spur  gear  rim,  arms,  and  hub 
Spiir  gears 
Stacks  and  casings 
Stands 
Steam  boilers 

sectional 

tubular 


Page 

507 
419 
487 
223 
441 
429 
432 
429 
433 
430 
434 
432 
175 
108 
135 
128 
273 
184 
'  232 
285 
232 


Steam-heating  boilers,  care  and  manage- 
ment 288 

Storm  overflows  462 

Stoves  197 

Strain,  definition  of  29 

Stress,  definition  of  29 

Structural  machinery  78 

Stub  tooth  1 38 

Studs  163,  172 

Sub-surface  irrigation  465 


Tables 

air  required  per  person  206 

air  required  for  ventilation  206 

ah-  changes  required  207 

air-flow  through  flues  282 

blow-off,  sizes  for  264 

boiler  data  234 

bolts,  strength  of  168 

cistern  capacity  481 

direct  hot-water  heating  data  307 

disc  fan  data  371 

effective  areas  of  fans  363 

fan  speeds  361 

feed  pipes,  sizes  for  264 

Note. — For  page  numbers  see  foot  of  pages. 


Tables 

flrepot  dimensions 
gas  pipe  data 
gear  design  data 
grate  area  data 


Page 

223 
505 
140 
233 


heat  loss,  factors  for  calculating  211 

heat  losses  in  B.  T.  U.  210 

heater  dimensions  351 
heating  surface  supplied  by  various 

sizes  of  pipe  260 

heating  systems,  relative  cost  of  200 

indirect  hot-water  heating  data  312 

indirect  radiating  surface  data  287 

keys,  proportions  for  180 

lead  pipe  474 

leather  belting,  sizes  of  98 

mains,  data  for  317 

oval  pipe  dimensions  228 

pipe  heater  data  350 

pipe  sizes  355 

pipe  sizes  from  boiler  to  main  header  263 

pipe  sizes  for  radiator  connections  262 
power  required  for  moving  air  under 

different  pressures  366 
radiating  surface  supplied  by  steam 

risers  261 

radiator  efficiency  243 

register  sizes  for  different  pipes  229 

return,  sizes  for  264 

return  pipe  sizes  262 
safe-working  stresses  for  different 

speeds  134 

steam  flow  257,  258 

tin-lined  lead  pipe  475 

torsional  moments  43 

warm-air  pipe  dimensions  226 

water  pressure  471,472 

wrought-iron  pipe  dimensions  473 

Tank  overflow  pipe  483 

Tanks  424 

Tap  bolts  172 

Telethermometer  389 

Te,mperature  regulators  385,  498 

Tension  25,  118 

Theoretical  design  20 

Thermostat  338,  386 

Through  bolts  172 


544 


INDEX 

VII 

Page 

Page 

Tidal  chambers 

462 

Ventilation 

Tile  pipes 

434 

horse-power  for 

238 

Torsion 

25,  117 

of  hospitals 

398 

Traps 

422,  436 

of  office  buildings 

403 

Tubular  boilers 

232 

principles  of 

203 

of  school  buildings 

392 

D 

of  sewers 

460 

Underdrains 

459 

of  theaters 

402 

Urinals 

416 

Vents 

436 

local 

440 

V 

soil  pipe 

441 

Vacuum  systems  of  heating 

337 

Paul  system 

341 

W 

Webster  system 

337 

Warm-air  flues 

277 

Valves 

254 

Warming  systems 

197 

Velocity  of  air,  measurements  of 

207 

Water  closets 

412 

Vent  flues 

279 

Water-seal  motor 

338 

Ventilation 

Water-tube  boilers 

235 

air  required  for 

205 

Web  gears 

139 

of  apartment  houses 

405 

Webster  vacuum  system  of  heating 

337 

of  churches 

400 

Woodruff  key 

179 

of  conservatories 

405 

Worm 

146 

of  greenhouses 

405 

Worm  gear 

146 

of  halls 

402 

Wrought  iron  pipe 

432 

Note.  —  For  page  numbers  see  foot  of 

pages. 

\v 

545 


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